Three-dimensional memory device with drain-select-level isolation structures and method of making the same

ABSTRACT

Electrical isolation between adjacent stripes of drain-select-level electrically conductive layers can be provided by forming a drain-select-level isolation structure between neighboring rows of memory stack structures. The drain-select-level isolation structure can partially cut through upper regions of the neighboring rows of memory stack structures. Vertical semiconductor channels of the neighboring rows of memory stack structures include a lower tubular segment and an upper semi-tubular segment that contact the drain-select-level isolation structure. Electrical current through drain select levels is limited to the semi-tubular segment of each vertical semiconductor channel. Alternatively, the drain-select-level isolation structure can be formed around the memory stack structures within the neighboring rows of memory stack structures. Ion implantation can be used to suppress conduction of electrical current through portions of vertical semiconductor channels that are proximal to the drain-select-level isolation structure.

FIELD

The present disclosure relates generally to the field of semiconductordevices, and particular to a three-dimensional memory device includingdrain-select-level isolation structures and methods of manufacturing thesame.

BACKGROUND

Three-dimensional vertical NAND strings having one bit per cell aredisclosed in an article by T. Endoh et al., titled “Novel Ultra HighDensity Memory With A Stacked-Surrounding Gate Transistor (S-SGT)Structured Cell”, IEDM Proc. (2001) 33-36.

SUMMARY

According to an aspect of the present disclosure, a three-dimensionalmemory device is provided, which comprises: an alternating stack ofinsulating layers and electrically conductive layers located over asubstrate; first memory stack structures extending through thealternating stack, wherein each of the first memory stack structuresincludes a respective first memory film and a respective first verticalsemiconductor channel; and a drain-select-level isolation structurehaving a pair of straight lengthwise sidewalls that extend along a firsthorizontal direction and contact straight sidewalls of the first memorystack structures, wherein each first vertical semiconductor channelcomprises a tubular section that underlie a horizontal plane including abottom surface of the drain-select-level isolation structure and asemi-tubular section overlying the tubular section and contacting thedrain-select-level isolation structure.

According to another aspect of the present disclosure, a method offorming a three-dimensional memory device is provided, which comprises:forming an alternating stack of insulating layers and spacer materiallayers over a substrate, wherein the spacer material layers are formedas, or are subsequently replaced with, electrically conductive layers;forming memory stack structures extending through the alternating stack,wherein each of the memory stack structures includes a respective memoryfilm and a respective vertical semiconductor channel including dopantsof a first conductivity type, wherein the memory stack structurescomprises first memory stack structures arranged in two rows that extendalong a first horizontal direction; forming a drain-select-level trenchby etching through an upper portion of the alternating stack and a firstarea of each of the first memory stack structures, wherein thedrain-select-level trench includes a pair of straight lengthwisesidewalls that extend along the first horizontal direction; and forminga drain-select-level isolation structure in the drain-select-leveltrench, wherein each vertical semiconductor channel within the firstmemory stack structures comprises a tubular section that underlie ahorizontal plane including a bottom surface of the drain-select-levelisolation structure and a semi-tubular section overlying the tubularsection and contacting the drain-select-level isolation structure.

According to yet another aspect of the present disclosure, athree-dimensional memory device is provided, which comprises: analternating stack of insulating layers and electrically conductivelayers located over a substrate; and first memory stack structuresextending through the alternating stack, wherein each of the firstmemory stack structures includes a respective first memory film and arespective first vertical semiconductor channel, wherein each firstvertical semiconductor channel comprises a tubular section includingdopants of a first conductivity type at a first atomic concentration, afirst semi-tubular section overlying the tubular section and includingdopants of the first conductivity type at the first atomicconcentration, and a second semi-tubular section overlying the tubularsection and laterally adjoined to the first semi-tubular section andincluding dopants of the first conductivity type at a second atomicconcentration that is greater than the first atomic concentration.

According to still another aspect of the present disclosure, a method offorming a three-dimensional memory device is provided, which comprises:forming an alternating stack of insulating layers and spacer materiallayers over a substrate, wherein the spacer material layers are formedas, or are subsequently replaced with, electrically conductive layers;forming memory stack structures extending through the alternating stack,wherein each of the memory stack structures includes a respective memoryfilm and a respective vertical semiconductor channel including dopantsof a first conductivity type at a first atomic concentration, whereinthe memory stack structures comprises first memory stack structuresarranged in two rows that extend along a first horizontal direction;partially physically exposing upper portions of sidewalls of the tworows of the first memory stack structures by forming adrain-select-level trench that extend through an upper portion of thealternating stack and laterally extending between the two rows of thefirst memory stack structures; and implanting dopants of the firstconductivity type into segments of vertical semiconductor channelswithin the first memory stack structures that are proximal to thedrain-select-level trench, wherein each vertical semiconductor channelwithin the first memory stack structures comprises a tubular sectionincluding dopants of the first conductivity type at the first atomicconcentration, a first semi-tubular section overlying the tubularsection and including dopants of the first conductivity type at thefirst atomic concentration, and a second semi-tubular section overlyingthe tubular section and laterally adjoined to the first semi-tubularsection and including dopants of the first conductivity type at a secondatomic concentration that is greater than the first atomicconcentration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical cross-sectional view of a first exemplarystructure after formation of at least one peripheral device, and asemiconductor material layer according to a first embodiment of thepresent disclosure.

FIG. 2 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of an alternating stack ofinsulating layers and sacrificial material layers according to the firstembodiment of the present disclosure.

FIG. 3 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of stepped terraces and aretro-stepped dielectric material portion according to the firstembodiment of the present disclosure.

FIG. 4A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of memory openings and supportopenings according to the first embodiment of the present disclosure.

FIG. 4B is a top-down view of the first exemplary structure of FIG. 4A.The zig-zag vertical plane A-A′ is the plane of the cross-section forFIG. 4A.

FIGS. 5A-5H are sequential schematic vertical cross-sectional views of amemory opening within the first exemplary structure during formation ofa memory stack structure, an optional dielectric core, and a drainregion therein according to the first embodiment of the presentdisclosure.

FIG. 6 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of memory stack structures andsupport pillar structures according to the first embodiment of thepresent disclosure.

FIG. 7A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of drain-select-level trenchesaccording to the first embodiment of the present disclosure.

FIG. 7B is a partial see-through top-down view of the first exemplarystructure of FIG. 7A. The zig-zag vertical plane A-A′ is the plane ofthe schematic vertical cross-sectional view of FIG. 7A.

FIG. 8A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of drain-select-level isolationstructures according to the first embodiment of the present disclosure.

FIG. 8B is a partial see-through top-down view of the first exemplarystructure of FIG. 7A. The zig-zag vertical plane A-A′ is the plane ofthe schematic vertical cross-sectional view of FIG. 7A.

FIG. 9A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of backside trenches according tothe first embodiment of the present disclosure.

FIG. 9B is a partial see-through top-down view of the first exemplarystructure of FIG. 7A. The zig-zag vertical plane A-A′ is the plane ofthe schematic vertical cross-sectional view of FIG. 7A.

FIG. 10 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of backside recesses according tothe first embodiment of the present disclosure.

FIGS. 11A-11D are sequential vertical cross-sectional views of a regionof the first exemplary structure during formation of electricallyconductive layers according to the first embodiment of the presentdisclosure.

FIG. 12 is a schematic vertical cross-sectional view of the firstexemplary structure at the processing step of FIG. 11D.

FIG. 13 is a schematic vertical cross-sectional view of the firstexemplary structure after removal of a deposited conductive materialfrom within the backside trench according to the first embodiment of thepresent disclosure.

FIG. 14A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of insulating spacers and backsidecontact via structures according to the first embodiment of the presentdisclosure.

FIG. 14B is a magnified view of a region of the first exemplarystructure of FIG. 14A.

FIG. 15A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of additional contact via structuresaccording to the first embodiment of the present disclosure.

FIG. 15B is a top-down view of the first exemplary structure of FIG.15A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 15A.

FIG. 16 is a vertical cross-sectional view of the first exemplarystructure after formation of interconnect-level dielectric materiallayers, additional metal interconnect structures, and bonding padsaccording to the first embodiment of the present disclosure.

FIG. 17 is a vertical cross-sectional view of a second exemplarystructure after formation of insulating spacers and backside contact viastructures according to a second embodiment of the present disclosure.

FIG. 18 is a vertical cross-sectional view of the second exemplarystructure after removal of a sacrificial planarization stopper layeraccording to the second embodiment of the present disclosure.

FIG. 19A is a vertical cross-section view of the second exemplarystructure during formation of drain-select-level trenches according tothe second embodiment of the present disclosure.

FIG. 19B is a top-down view of the second exemplary structure of FIG.19A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 19A.

FIG. 20 is a vertical cross-section view of the second exemplarystructure after formation of drain-select-level trenches according tothe second embodiment of the present disclosure.

FIG. 21 is a vertical cross-section view of the second exemplarystructure after formation of drain-select-level isolation structures anda contact level dielectric layer according to the second embodiment ofthe present disclosure.

FIG. 22A is a schematic vertical cross-sectional view of the secondexemplary structure after formation of additional contact via structuresaccording to the second embodiment of the present disclosure.

FIG. 22B is a top-down view of the second exemplary structure of FIG.22A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 22A.

FIG. 23 is a vertical cross-section view of an alternative embodiment ofthe second exemplary structure during formation of drain-select-leveltrenches according to the second embodiment of the present disclosure.

FIG. 24 is a vertical cross-section view of the alternative embodimentof the second exemplary structure after formation of drain-select-leveltrenches according to the second embodiment of the present disclosure.

FIG. 25A is a vertical cross-sectional view of a third exemplarystructure after formation of an alternating stack and a retro-steppeddielectric material portion according to a third embodiment of thepresent disclosure.

FIG. 25B is a vertical cross-sectional view of an in-process sourcelevel material layers according to the third embodiment of the presentdisclosure.

FIG. 26A is a vertical cross-sectional view of the third exemplarystructure after formation of memory openings and support openingsaccording to the third embodiment of the present disclosure.

FIG. 26B is a top-down view of the third exemplary structure of FIG.26A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 26A.

FIG. 27 is a vertical cross-sectional view of the third exemplarystructure after formation of memory stack structures according to thethird embodiment of the present disclosure.

FIG. 28A is a vertical cross-sectional view of the third exemplarystructure after formation of drain-select-level trenches according tothe third embodiment of the present disclosure.

FIG. 28B is a top-down view of the third exemplary structure of FIG.28A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 28A.

FIG. 29A is a vertical cross-sectional view of the third exemplarystructure after formation of drain-select-level isolation structuresaccording to the third embodiment of the present disclosure.

FIG. 29B is a top-down view of the third exemplary structure of FIG.29A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 29A.

FIG. 30A is a vertical cross-sectional view of the third exemplarystructure after formation of backside trenches according to the thirdembodiment of the present disclosure.

FIG. 30B is a top-down view of the third exemplary structure of FIG.30A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 30A.

FIGS. 31A-31E are sequential vertical cross-sectional views of abackside trench and two memory opening fill structures duringreplacement of the in-process source level material layers with sourcelevel material layers according to the third embodiment of the presentdisclosure.

FIG. 32 is a schematic vertical cross-sectional view of the thirdexemplary structure after formation of backside recesses according tothe third embodiment of the present disclosure.

FIG. 33 is a schematic vertical cross-sectional view of the thirdexemplary structure after formation of electrically conductive layersaccording to the third embodiment of the present disclosure.

FIG. 34 is a schematic vertical cross-sectional view of the thirdexemplary structure after formation of dielectric wall structuresaccording to the third embodiment of the present disclosure.

FIG. 35A is a schematic vertical cross-sectional view of the thirdexemplary structure after removal of a sacrificial planarization stopperlayer according to the third embodiment of the present disclosure.

FIG. 35B is a top-down view of the third exemplary structure of FIG.35A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 35A.

FIG. 36 is a schematic vertical cross-sectional view of the thirdexemplary structure after formation of drain-select-level recessesaccording to the third embodiment of the present disclosure.

FIG. 37A is a schematic vertical cross-sectional view of the thirdexemplary structure after formation of a drain-select-level electricallyconductive layer according to the third embodiment of the presentdisclosure.

FIG. 37B is a top-down view of the third exemplary structure of FIG.37A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 37A.

FIG. 38A is a schematic vertical cross-sectional view of the thirdexemplary structure after formation of additional contact via structuresaccording to the third embodiment of the present disclosure.

FIG. 38B is a top-down view of the third exemplary structure of FIG.38A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 38A.

FIG. 39A is a vertical cross-sectional view of a fourth exemplarystructure after formation of drain-select-level trenches according to afourth embodiment of the present disclosure.

FIG. 39B is a top-down view of the fourth exemplary structure of FIG.39A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 39A.

FIG. 40A is a vertical cross-sectional view of the fourth exemplarystructure after ion implantation of dopants of a first conductivity typeinto portions of vertical semiconductor channels according to the fourthembodiment of the present disclosure.

FIG. 40B is horizontal cross-sectional view of a drain region at theprocessing steps of FIG. 40A.

FIG. 41A is a vertical cross-sectional view of the fourth exemplarystructure after formation of drain-select-level isolation structuresaccording to the fourth embodiment of the present disclosure.

FIG. 41B is a top-down view of the third exemplary structure of FIG.41A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 41A.

FIG. 42 is a vertical cross-sectional view of the fourth exemplarystructure after formation of a contact level dielectric layer accordingto the fourth embodiment of the present disclosure.

FIG. 43A is a schematic vertical cross-sectional view of the fourthexemplary structure after formation of additional contact via structuresaccording to the fourth embodiment of the present disclosure.

FIG. 43B is a top-down view of the fourth exemplary structure of FIG.43A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 43A.

FIG. 43C is a horizontal cross-sectional view of the fourth exemplarystructure along the horizontal plane C-C′ of FIG. 43A.

FIG. 44A is a vertical cross-sectional view of a fifth exemplarystructure after formation of drain-select-level trenches according to afifth embodiment of the present disclosure.

FIG. 44B is a top-down view of the fifth exemplary structure of FIG.44A. The zig-zag vertical plane A-A′ is the plane of the schematicvertical cross-sectional view of FIG. 44A.

FIG. 45 is a vertical cross-sectional view of the fourth exemplarystructure after ion implantation of dopants of a first conductivity typeinto portions of vertical semiconductor channels according to the fifthembodiment of the present disclosure.

FIG. 46 is a vertical cross-sectional view of the fourth exemplarystructure formation of backside trenches according to the fifthembodiment of the present disclosure.

FIG. 47 is a vertical cross-sectional view of the fourth exemplarystructure after replacement of the sacrificial material layers withelectrically conductive layers according to the fifth embodiment of thepresent disclosure.

DETAILED DESCRIPTION

As discussed above, the present disclosure is directed tothree-dimensional memory devices including a vertical stack ofmultilevel memory arrays and methods of making thereof, the variousaspects of which are described below. The embodiments of the disclosurecan be used to form various structures including a multilevel memorystructure, non-limiting examples of which include semiconductor devicessuch as three-dimensional monolithic memory array devices comprising aplurality of NAND memory strings.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are used merely to identify similar elements, and differentordinals may be used across the specification and the claims of theinstant disclosure. The same reference numerals refer to the sameelement or similar element. Unless otherwise indicated, elements havingthe same reference numerals are presumed to have the same compositionand the same function. Unless otherwise indicated, a “contact” betweenelements refers to a direct contact between elements that provides anedge or a surface shared by the elements. As used herein, a firstelement located “on” a second element can be located on the exteriorside of a surface of the second element or on the interior side of thesecond element. As used herein, a first element is located “directly on”a second element if there exist a physical contact between a surface ofthe first element and a surface of the second element. As used herein, a“prototype” structure or an “in-process” structure refers to a transientstructure that is subsequently modified in the shape or composition ofat least one component therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, or may have one or more layer thereupon, thereabove,and/or therebelow.

As used herein, a first surface and a second surface are “verticallycoincident” with each other if the second surface overlies or underliesthe first surface and there exists a zig-zag vertical plane or asubstantially zig-zag vertical plane that includes the first surface andthe second surface. A substantially zig-zag vertical plane is a planethat extends straight along a direction that deviates from a verticaldirection by an angle less than 5 degrees. A zig-zag vertical plane or asubstantially zig-zag vertical plane is straight along a verticaldirection or a substantially vertical direction, and may, or may not,include a curvature along a direction that is perpendicular to thevertical direction or the substantially vertical direction.

A monolithic three-dimensional memory array is a memory array in whichmultiple memory levels are formed above a single substrate, such as asemiconductor wafer, with no intervening substrates. The term“monolithic” means that layers of each level of the array are directlydeposited on the layers of each underlying level of the array. Incontrast, two dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device. For example,non-monolithic stacked memories have been constructed by forming memorylevels on separate substrates and vertically stacking the memory levels,as described in U.S. Pat. No. 5,915,167 titled “Three-dimensionalStructure Memory.” The substrates may be thinned or removed from thememory levels before bonding, but as the memory levels are initiallyformed over separate substrates, such memories are not true monolithicthree-dimensional memory arrays. The various three-dimensional memorydevices of the present disclosure include a monolithic three-dimensionalNAND string memory device, and can be fabricated using the variousembodiments described herein.

Generally, a semiconductor package (or a “package”) refers to a unitsemiconductor device that can be attached to a circuit board through aset of pins or solder balls. A semiconductor package may include asemiconductor chip (or a “chip”) or a plurality of semiconductor chipsthat are bonded thereamongst, for example, by flip-chip bonding oranother chip-to-chip bonding. A package or a chip may include a singlesemiconductor die (or a “die”) or a plurality of semiconductor dies. Adie is the smallest unit that can independently execute externalcommands or report status. Typically, a package or a chip with multipledies is capable of simultaneously executing as many external commands asthe total number of planes therein. Each die includes one or moreplanes. Identical concurrent operations can be executed in each planewithin a same die, although there may be some restrictions. In case adie is a memory die, i.e., a die including memory elements, concurrentread operations, concurrent write operations, or concurrent eraseoperations can be performed in each plane within a same memory die. In amemory die, each plane contains a number of memory blocks (or “blocks”),which are the smallest unit that can be erased by in a single eraseoperation. Each memory block contains a number of pages, which are thesmallest units that can be selected for programming. A page is also thesmallest unit that can be selected to a read operation.

Referring to FIG. 1, a first exemplary structure according to the firstembodiment of the present disclosure is illustrated, which can be used,for example, to fabricate a device structure containing vertical NANDmemory devices. The first exemplary structure includes a substrate (9,10), which can be a semiconductor substrate. The substrate can include asubstrate semiconductor layer 9 and an optional semiconductor materiallayer 10. The substrate semiconductor layer 9 maybe a semiconductorwafer or a semiconductor material layer, and can include at least oneelemental semiconductor material (e.g., single crystal silicon wafer orlayer), at least one III-V compound semiconductor material, at least oneII-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. The substrate can have a major surface 7, which can be, forexample, a topmost surface of the substrate semiconductor layer 9. Themajor surface 7 can be a semiconductor surface. In one embodiment, themajor surface 7 can be a single crystalline semiconductor surface, suchas a single crystalline semiconductor surface.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0 S/m in theabsence of electrical dopants therein, and is capable of producing adoped material having electrical conductivity in a range from 1.0 S/m to1.0×10⁵ S/m upon suitable doping with an electrical dopant. As usedherein, an “electrical dopant” refers to a p-type dopant that adds ahole to a valence band within a band structure, or an n-type dopant thatadds an electron to a conduction band within a band structure. As usedherein, a “conductive material” refers to a material having electricalconductivity greater than 1.0×10⁵ S/m. As used herein, an “insulatormaterial” or a “dielectric material” refers to a material havingelectrical conductivity less than 1.0×10⁻⁵ S/m. As used herein, a“heavily doped semiconductor material” refers to a semiconductormaterial that is doped with electrical dopant at a sufficiently highatomic concentration to become a conductive material either as formed asa crystalline material or if converted into a crystalline materialthrough an anneal process (for example, from an initial amorphousstate), i.e., to have electrical conductivity greater than 1.0×10⁵ S/m.A “doped semiconductor material” may be a heavily doped semiconductormaterial, or may be a semiconductor material that includes electricaldopants (i.e., p-type dopants and/or n-type dopants) at a concentrationthat provides electrical conductivity in the range from 1.0×10⁻⁵ S/m to1.0×10⁵ S/m. An “intrinsic semiconductor material” refers to asemiconductor material that is not doped with electrical dopants. Thus,a semiconductor material may be semiconducting or conductive, and may bean intrinsic semiconductor material or a doped semiconductor material. Adoped semiconductor material can be semiconducting or conductivedepending on the atomic concentration of electrical dopants therein. Asused herein, a “metallic material” refers to a conductive materialincluding at least one metallic element therein. All measurements forelectrical conductivities are made at the standard condition.

At least one semiconductor device 700 for a peripheral circuitry can beoptionally formed on a portion of the substrate semiconductor layer 9.The at least one semiconductor device can include, for example, fieldeffect transistors. For example, at least one shallow trench isolationstructure 720 can be formed by etching portions of the substratesemiconductor layer 9 and depositing a dielectric material therein. Agate dielectric layer, at least one gate conductor layer, and a gate capdielectric layer can be formed over the substrate semiconductor layer 9,and can be subsequently patterned to form at least one gate structure(750, 752, 754, 758), each of which can include a gate dielectric 750, agate electrode (752, 754), and a gate cap dielectric 758. The gateelectrode (752, 754) may include a stack of a first gate electrodeportion 752 and a second gate electrode portion 754. At least one gatespacer 756 can be formed around the at least one gate structure (750,752, 754, 758) by depositing and anisotropically etching a dielectricliner. Active regions 730 can be formed in upper portions of thesubstrate semiconductor layer 9, for example, by introducing electricaldopants using the at least one gate structure (750, 752, 754, 758) asmasking structures. Additional masks may be used as needed. The activeregion 730 can include source regions and drain regions of field effecttransistors. A first dielectric liner 761 and a second dielectric liner762 can be optionally formed. Each of the first and second dielectricliners (761, 762) can comprise a silicon oxide layer, a silicon nitridelayer, and/or a dielectric metal oxide layer. As used herein, siliconoxide includes silicon dioxide as well as non-stoichiometric siliconoxides having more or less than two oxygen atoms for each silicon atoms.Silicon dioxide is preferred. In an illustrative example, the firstdielectric liner 761 can be a silicon oxide layer, and the seconddielectric liner 762 can be a silicon nitride layer. The least onesemiconductor device for the peripheral circuitry can contain a drivercircuit for memory devices to be subsequently formed, which can includeat least one NAND device.

A dielectric material such as silicon oxide can be deposited over the atleast one semiconductor device, and can be subsequently planarized toform a planarization dielectric layer 770. In one embodiment theplanarized top surface of the planarization dielectric layer 770 can becoplanar with a top surface of the dielectric liners (761, 762).Subsequently, the planarization dielectric layer 770 and the dielectricliners (761, 762) can be removed from an area to physically expose a topsurface of the substrate semiconductor layer 9. As used herein, asurface is “physically exposed” if the surface is in physical contactwith vacuum, or a gas phase material (such as air).

The optional semiconductor material layer 10, if present, can be formedon the top surface of the substrate semiconductor layer 9 prior to, orafter, formation of the at least one semiconductor device 700 bydeposition of a single crystalline semiconductor material, for example,by selective epitaxy. The deposited semiconductor material can be thesame as, or can be different from, the semiconductor material of thesubstrate semiconductor layer 9. The deposited semiconductor materialcan be any material that can be used for the substrate semiconductorlayer 9 as described above. The single crystalline semiconductormaterial of the semiconductor material layer 10 can be in epitaxialalignment with the single crystalline structure of the substratesemiconductor layer 9. Portions of the deposited semiconductor materiallocated above the top surface of the planarization dielectric layer 770can be removed, for example, by chemical mechanical planarization (CMP).In this case, the semiconductor material layer 10 can have a top surfacethat is coplanar with the top surface of the planarization dielectriclayer 770.

The region (i.e., area) of the at least one semiconductor device 700 isherein referred to as a peripheral device region 200. The region inwhich a memory array is subsequently formed is herein referred to as amemory array region 100. A staircase region 300 for subsequently formingstepped terraces of electrically conductive layers can be providedbetween the memory array region 100 and the peripheral device region200.

Referring to FIG. 2, a stack of an alternating plurality of firstmaterial layers (which can be insulating layers 32) and second materiallayers (which can be sacrificial material layer 42) is formed over thetop surface of the substrate (9, 10). As used herein, a “material layer”refers to a layer including a material throughout the entirety thereof.As used herein, an alternating plurality of first elements and secondelements refers to a structure in which instances of the first elementsand instances of the second elements alternate. Each instance of thefirst elements that is not an end element of the alternating pluralityis adjoined by two instances of the second elements on both sides, andeach instance of the second elements that is not an end element of thealternating plurality is adjoined by two instances of the first elementson both ends. The first elements may have the same thicknessthereamongst, or may have different thicknesses. The second elements mayhave the same thickness thereamongst, or may have different thicknesses.The alternating plurality of first material layers and second materiallayers may begin with an instance of the first material layers or withan instance of the second material layers, and may end with an instanceof the first material layers or with an instance of the second materiallayers. In one embodiment, an instance of the first elements and aninstance of the second elements may form a unit that is repeated withperiodicity within the alternating plurality.

Each first material layer includes a first material, and each secondmaterial layer includes a second material that is different from thefirst material. In one embodiment, each first material layer can be aninsulating layer 32, and each second material layer can be a sacrificialmaterial layer. In this case, the stack can include an alternatingplurality of insulating layers 32 and sacrificial material layers 42,and constitutes a prototype stack of alternating layers comprisinginsulating layers 32 and sacrificial material layers 42.

The stack of the alternating plurality is herein referred to as analternating stack (32, 42). In one embodiment, the alternating stack(32, 42) can include insulating layers 32 composed of the firstmaterial, and sacrificial material layers 42 composed of a secondmaterial different from that of insulating layers 32. The first materialof the insulating layers 32 can be at least one insulating material. Assuch, each insulating layer 32 can be an insulating material layer.Insulating materials that can be used for the insulating layers 32include, but are not limited to, silicon oxide (including doped orundoped silicate glass), silicon nitride, silicon oxynitride,organosilicate glass (OSG), spin-on dielectric materials, dielectricmetal oxides that are commonly known as high dielectric constant(high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.)and silicates thereof, dielectric metal oxynitrides and silicatesthereof, and organic insulating materials. In one embodiment, the firstmaterial of the insulating layers 32 can be silicon oxide.

The second material of the sacrificial material layers 42 is asacrificial material that can be removed selective to the first materialof the insulating layers 32. As used herein, a removal of a firstmaterial is “selective to” a second material if the removal processremoves the first material at a rate that is at least twice the rate ofremoval of the second material. The ratio of the rate of removal of thefirst material to the rate of removal of the second material is hereinreferred to as a “selectivity” of the removal process for the firstmaterial with respect to the second material.

The sacrificial material layers 42 may comprise an insulating material,a semiconductor material, or a conductive material. The second materialof the sacrificial material layers 42 can be subsequently replaced withelectrically conductive electrodes which can function, for example, ascontrol gate electrodes of a vertical NAND device. Non-limiting examplesof the second material include silicon nitride, an amorphoussemiconductor material (such as amorphous silicon), and apolycrystalline semiconductor material (such as polysilicon). In oneembodiment, the sacrificial material layers 42 can be spacer materiallayers that comprise silicon nitride or a semiconductor materialincluding at least one of silicon and germanium.

In one embodiment, the insulating layers 32 can include silicon oxide,and sacrificial material layers can include silicon nitride sacrificialmaterial layers. The first material of the insulating layers 32 can bedeposited, for example, by chemical vapor deposition (CVD). For example,if silicon oxide is used for the insulating layers 32, tetraethylorthosilicate (TEOS) can be used as the precursor material for the CVDprocess. The second material of the sacrificial material layers 42 canbe formed, for example, CVD or atomic layer deposition (ALD).

The sacrificial material layers 42 can be suitably patterned so thatconductive material portions to be subsequently formed by replacement ofthe sacrificial material layers 42 can function as electricallyconductive electrodes, such as the control gate electrodes of themonolithic three-dimensional NAND string memory devices to besubsequently formed. The sacrificial material layers 42 may comprise aportion having a strip shape extending substantially parallel to themajor surface 7 of the substrate.

The thicknesses of the insulating layers 32 and the sacrificial materiallayers 42 can be in a range from 20 nm to 50 nm, although lesser andgreater thicknesses can be used for each insulating layer 32 and foreach sacrificial material layer 42. The number of repetitions of thepairs of an insulating layer 32 and a sacrificial material layer (e.g.,a control gate electrode or a sacrificial material layer) 42 can be in arange from 2 to 1,024, and typically from 8 to 256, although a greaternumber of repetitions can also be used. The top and bottom gateelectrodes in the stack may function as the select gate electrodes. Inone embodiment, each sacrificial material layer 42 in the alternatingstack (32, 42) can have a uniform thickness that is substantiallyinvariant within each respective sacrificial material layer 42.

While the present disclosure is described using an embodiment in whichthe spacer material layers are sacrificial material layers 42 that aresubsequently replaced with electrically conductive layers, in otherembodiments the sacrificial material layers are formed as electricallyconductive layers. In this case, steps for replacing the spacer materiallayers with electrically conductive layers can be omitted.

Optionally, an insulating cap layer 70 can be formed over thealternating stack (32, 42). The insulating cap layer 70 includes adielectric material that is different from the material of thesacrificial material layers 42. In one embodiment, the insulating caplayer 70 can include a dielectric material that can be used for theinsulating layers 32 as described above. The insulating cap layer 70 canhave a greater thickness than each of the insulating layers 32. Theinsulating cap layer 70 can be deposited, for example, by chemical vapordeposition. In one embodiment, the insulating cap layer 70 can be asilicon oxide layer.

Referring to FIG. 3, stepped surfaces are formed at a peripheral regionof the alternating stack (32, 42), which is herein referred to as aterrace region. As used herein, “stepped surfaces” refer to a set ofsurfaces that include at least two horizontal surfaces and at least twovertical surfaces such that each horizontal surface is adjoined to afirst vertical surface that extends upward from a first edge of thehorizontal surface, and is adjoined to a second vertical surface thatextends downward from a second edge of the horizontal surface. A steppedcavity is formed within the volume from which portions of thealternating stack (32, 42) are removed through formation of the steppedsurfaces. A “stepped cavity” refers to a cavity having stepped surfaces.

The terrace region is formed in the staircase region 300, which islocated between the memory array region 100 and the peripheral deviceregion 200 containing the at least one semiconductor device for theperipheral circuitry. The stepped cavity can have various steppedsurfaces such that the horizontal cross-sectional shape of the steppedcavity changes in steps as a function of the vertical distance from thetop surface of the substrate (9, 10). In one embodiment, the steppedcavity can be formed by repetitively performing a set of processingsteps. The set of processing steps can include, for example, an etchprocess of a first type that vertically increases the depth of a cavityby one or more levels, and an etch process of a second type thatlaterally expands the area to be vertically etched in a subsequent etchprocess of the first type. As used herein, a “level” of a structureincluding alternating plurality is defined as the relative position of apair of a first material layer and a second material layer within thestructure.

Each sacrificial material layer 42 other than a topmost sacrificialmaterial layer 42 within the alternating stack (32, 42) laterallyextends farther than any overlying sacrificial material layer 42 withinthe alternating stack (32, 42) in the terrace region. The terrace regionincludes stepped surfaces of the alternating stack (32, 42) thatcontinuously extend from a bottommost layer within the alternating stack(32, 42) to a topmost layer within the alternating stack (32, 42).

Each vertical step of the stepped surfaces can have the height of one ormore pairs of an insulating layer 32 and a sacrificial material layer.In one embodiment, each vertical step can have the height of a singlepair of an insulating layer 32 and a sacrificial material layer 42. Inanother embodiment, multiple “columns” of staircases can be formed alonga first horizontal direction hd1 such that each vertical step has theheight of a plurality of pairs of an insulating layer 32 and asacrificial material layer 42, and the number of columns can be at leastthe number of the plurality of pairs. Each column of staircase can bevertically offset among one another such that each of the sacrificialmaterial layers 42 has a physically exposed top surface in a respectivecolumn of staircases. In the illustrative example, two columns ofstaircases are formed for each block of memory stack structures to besubsequently formed such that one column of staircases providephysically exposed top surfaces for odd-numbered sacrificial materiallayers 42 (as counted from the bottom) and another column of staircasesprovide physically exposed top surfaces for even-numbered sacrificialmaterial layers (as counted from the bottom). Configurations usingthree, four, or more columns of staircases with a respective set ofvertical offsets among the physically exposed surfaces of thesacrificial material layers 42 may also be used. Each sacrificialmaterial layer 42 has a greater lateral extent, at least along onedirection, than any overlying sacrificial material layers 42 such thateach physically exposed surface of any sacrificial material layer 42does not have an overhang. In one embodiment, the vertical steps withineach column of staircases may be arranged along the first horizontaldirection hd1, and the columns of staircases may be arranged along asecond horizontal direction hd2 that is perpendicular to the firsthorizontal direction hd1. In one embodiment, the first horizontaldirection hd1 may be perpendicular to the boundary between the memoryarray region 100 and the staircase region 300.

A retro-stepped dielectric material portion 65 (i.e., an insulating fillmaterial portion) can be formed in the stepped cavity by deposition of adielectric material therein. For example, a dielectric material such assilicon oxide can be deposited in the stepped cavity. Excess portions ofthe deposited dielectric material can be removed from above the topsurface of the insulating cap layer 70, for example, by chemicalmechanical planarization (CMP). The remaining portion of the depositeddielectric material filling the stepped cavity constitutes theretro-stepped dielectric material portion 65. As used herein, a“retro-stepped” element refers to an element that has stepped surfacesand a horizontal cross-sectional area that increases monotonically as afunction of a vertical distance from a top surface of a substrate onwhich the element is present. If silicon oxide is used for theretro-stepped dielectric material portion 65, the silicon oxide of theretro-stepped dielectric material portion 65 may, or may not, be dopedwith dopants such as B, P, and/or F.

Referring to FIGS. 4A and 4B, a lithographic material stack (not shown)including at least a photoresist layer can be formed over the insulatingcap layer 70 and the retro-stepped dielectric material portion 65, andcan be lithographically patterned to form openings therein. The openingsinclude a first set of openings formed over the memory array region 100and a second set of openings formed over the staircase region 300. Thepattern in the lithographic material stack can be transferred throughthe insulating cap layer 70 or the retro-stepped dielectric materialportion 65, and through the alternating stack (32, 42) by at least oneanisotropic etch that uses the patterned lithographic material stack asan etch mask layer. Portions of the alternating stack (32, 42)underlying the openings in the patterned lithographic material stack areetched to form memory openings 49 and support openings 19. As usedherein, a “memory opening” refers to a structure in which memoryelements, such as a memory stack structure, is subsequently formed. Asused herein, a “support opening” refers to a structure in which asupport structure (such as a support pillar structure) that mechanicallysupports other elements is subsequently formed. The memory openings 49are formed through the insulating cap layer 70 and the entirety of thealternating stack (32, 42) in the memory array region 100. The supportopenings 19 are formed through the retro-stepped dielectric materialportion 65 and the portion of the alternating stack (32, 42) thatunderlie the stepped surfaces in the staircase region 300.

The memory openings 49 extend through the entirety of the alternatingstack (32, 42). The support openings 19 extend through a subset oflayers within the alternating stack (32, 42). The chemistry of theanisotropic etch process used to etch through the materials of thealternating stack (32, 42) can alternate to optimize etching of thefirst and second materials in the alternating stack (32, 42). Theanisotropic etch can be, for example, a series of reactive ion etches.The sidewalls of the memory openings 49 and the support openings 19 canbe substantially vertical, or can be tapered. The patterned lithographicmaterial stack can be subsequently removed, for example, by ashing.

The memory openings 49 and the support openings 19 can extend from thetop surface of the alternating stack (32, 42) to at least the horizontalplane including the topmost surface of the semiconductor material layer10. In one embodiment, an overetch into the semiconductor material layer10 may be optionally performed after the top surface of thesemiconductor material layer 10 is physically exposed at a bottom ofeach memory opening 49 and each support opening 19. The overetch may beperformed prior to, or after, removal of the lithographic materialstack. In other words, the recessed surfaces of the semiconductormaterial layer 10 may be vertically offset from the un-recessed topsurfaces of the semiconductor material layer 10 by a recess depth. Therecess depth can be, for example, in a range from 1 nm to 50 nm,although lesser and greater recess depths can also be used. The overetchis optional, and may be omitted. If the overetch is not performed, thebottom surfaces of the memory openings 49 and the support openings 19can be coplanar with the topmost surface of the semiconductor materiallayer 10.

Each of the memory openings 49 and the support openings 19 may include asidewall (or a plurality of sidewalls) that extends substantiallyperpendicular to the topmost surface of the substrate. A two-dimensionalarray of memory openings 49 can be formed in the memory array region100. A two-dimensional array of support openings 19 can be formed in thestaircase region 300. The substrate semiconductor layer 9 and thesemiconductor material layer 10 collectively constitutes a substrate (9,10), which can be a semiconductor substrate. Alternatively, thesemiconductor material layer 10 may be omitted, and the memory openings49 and the support openings 19 can be extend to a top surface of thesubstrate semiconductor layer 9.

The memory openings 49 can be arrange in rows that extend along a firsthorizontal direction hd1 and laterally spaced apart along a secondhorizontal direction hd2 that is perpendicular to the first horizontaldirection hd1. Memory openings 49 in each row can have a uniformintra-row pitch p1, which is the center-to-center distance between aneighboring pair of memory openings 49 within a row of memory openings49. Further, the rows of memory openings 49 can be arranged along thesecond horizontal direction hd2 with a uniform inter-row pitch p2, or arow-to-row pitch, which is the distance between a first vertical planepassing through geometrical centers of a first row of memory openings 49and a second vertical plane passing through geometrical centers of asecond row of memory openings 49 that neighbors the first row of memoryopenings 49. In one embodiment, the memory openings 49 can be arrangedas two-dimensional periodic arrays that are laterally spaced apart alongthe second horizontal direction hd2. Each two-dimensional periodic arrayof memory openings 49 can include multiple rows of memory openings 49such that each neighboring pair of rows of memory openings 49 has auniform inter-row pitch p2. The number of rows of memory openings 49within each two-dimensional periodic array of memory openings 49 can bein a range from 4 to 32, such as from 8 to 16, although lesser andgreater number of rows may be used for each two-dimensional periodicarray of memory openings 49.

FIGS. 5A-5H illustrate structural changes in a memory opening 49, whichis one of the memory openings 49 in the first exemplary structure ofFIGS. 4A and 4B. The same structural change occurs simultaneously ineach of the other memory openings 49 and in each of the support openings19.

Referring to FIG. 5A, a memory opening 49 in the exemplary devicestructure of FIGS. 4A and 4B is illustrated. The memory opening 49extends through the insulating cap layer 70, the alternating stack (32,42), and optionally into an upper portion of the semiconductor materiallayer 10. At this processing step, each support opening 19 can extendthrough the retro-stepped dielectric material portion 65, a subset oflayers in the alternating stack (32, 42), and optionally through theupper portion of the semiconductor material layer 10. The recess depthof the bottom surface of each memory opening with respect to the topsurface of the semiconductor material layer 10 can be in a range from 0nm to 30 nm, although greater recess depths can also be used.Optionally, the sacrificial material layers 42 can be laterally recessedpartially to form lateral recesses (not shown), for example, by anisotropic etch.

Referring to FIG. 5B, an optional pedestal channel portion (e.g., anepitaxial pedestal) 11 can be formed at the bottom portion of eachmemory opening 49 and each support openings 19, for example, byselective epitaxy. Each pedestal channel portion 11 comprises a singlecrystalline semiconductor material in epitaxial alignment with thesingle crystalline semiconductor material of the semiconductor materiallayer 10. In one embodiment, the top surface of each pedestal channelportion 11 can be formed above a horizontal plane including the topsurface of a bottommost sacrificial material layer 42. In this case, asource select gate electrode can be subsequently formed by replacing thebottommost sacrificial material layer 42 with a conductive materiallayer. The pedestal channel portion 11 can be a portion of a transistorchannel that extends between a source region to be subsequently formedin the substrate (9, 10) and a drain region to be subsequently formed inan upper portion of the memory opening 49. A memory cavity 49′ ispresent in the unfilled portion of the memory opening 49 above thepedestal channel portion 11. In one embodiment, the pedestal channelportion 11 can comprise single crystalline silicon. In one embodiment,the pedestal channel portion 11 can have a doping of the firstconductivity type, which is the same as the conductivity type of thesemiconductor material layer 10 that the pedestal channel portioncontacts. If a semiconductor material layer 10 is not present, thepedestal channel portion 11 can be formed directly on the substratesemiconductor layer 9, which can have a doping of the first conductivitytype.

Referring to FIG. 5C, a stack of layers including a blocking dielectriclayer 52, a charge storage layer 54, a tunneling dielectric layer 56,and an optional first semiconductor channel layer 601 can besequentially deposited in the memory openings 49.

The blocking dielectric layer 52 can include a single dielectricmaterial layer or a stack of a plurality of dielectric material layers.In one embodiment, the blocking dielectric layer can include adielectric metal oxide layer consisting essentially of a dielectricmetal oxide. As used herein, a dielectric metal oxide refers to adielectric material that includes at least one metallic element and atleast oxygen. The dielectric metal oxide may consist essentially of theat least one metallic element and oxygen, or may consist essentially ofthe at least one metallic element, oxygen, and at least one non-metallicelement such as nitrogen. In one embodiment, the blocking dielectriclayer 52 can include a dielectric metal oxide having a dielectricconstant greater than 7.9, i.e., having a dielectric constant greaterthan the dielectric constant of silicon nitride.

Non-limiting examples of dielectric metal oxides include aluminum oxide(Al₂O₃), hafnium oxide (HfO₂), lanthanum oxide (LaO₂), yttrium oxide(Y₂O₃), tantalum oxide (Ta₂O₅), silicates thereof, nitrogen-dopedcompounds thereof, alloys thereof, and stacks thereof. The dielectricmetal oxide layer can be deposited, for example, by chemical vapordeposition (CVD), atomic layer deposition (ALD), pulsed laser deposition(PLD), liquid source misted chemical deposition, or a combinationthereof. The thickness of the dielectric metal oxide layer can be in arange from 1 nm to 20 nm, although lesser and greater thicknesses canalso be used. The dielectric metal oxide layer can subsequently functionas a dielectric material portion that blocks leakage of storedelectrical charges to control gate electrodes. In one embodiment, theblocking dielectric layer 52 includes aluminum oxide. In one embodiment,the blocking dielectric layer 52 can include multiple dielectric metaloxide layers having different material compositions.

Alternatively or additionally, the blocking dielectric layer 52 caninclude a dielectric semiconductor compound such as silicon oxide,silicon oxynitride, silicon nitride, or a combination thereof. In oneembodiment, the blocking dielectric layer 52 can include silicon oxide.In this case, the dielectric semiconductor compound of the blockingdielectric layer 52 can be formed by a conformal deposition method suchas low pressure chemical vapor deposition, atomic layer deposition, or acombination thereof. The thickness of the dielectric semiconductorcompound can be in a range from 1 nm to 20 nm, although lesser andgreater thicknesses can also be used. Alternatively, the blockingdielectric layer 52 can be omitted, and a backside blocking dielectriclayer can be formed after formation of backside recesses on surfaces ofmemory films to be subsequently formed.

Subsequently, the charge storage layer 54 can be formed. In oneembodiment, the charge storage layer 54 can be a continuous layer orpatterned discrete portions of a charge trapping material including adielectric charge trapping material, which can be, for example, siliconnitride. Alternatively, the charge storage layer 54 can include acontinuous layer or patterned discrete portions of a conductive materialsuch as doped polysilicon or a metallic material that is patterned intomultiple electrically isolated portions (e.g., floating gates), forexample, by being formed within lateral recesses into sacrificialmaterial layers 42. In one embodiment, the charge storage layer 54includes a silicon nitride layer. In one embodiment, the sacrificialmaterial layers 42 and the insulating layers 32 can have verticallycoincident sidewalls, and the charge storage layer 54 can be formed as asingle continuous layer.

In another embodiment, the sacrificial material layers 42 can belaterally recessed with respect to the sidewalls of the insulatinglayers 32, and a combination of a deposition process and an anisotropicetch process can be used to form the charge storage layer 54 as aplurality of memory material portions that are vertically spaced apart.While the present disclosure is described using an embodiment in whichthe charge storage layer 54 is a single continuous layer, in otherembodiments the charge storage layer 54 is replaced with a plurality ofmemory material portions (which can be charge trapping material portionsor electrically isolated conductive material portions) that arevertically spaced apart.

The charge storage layer 54 can be formed as a single charge storagelayer of homogeneous composition, or can include a stack of multiplecharge storage layers. The multiple charge storage layers, if used, cancomprise a plurality of spaced-apart floating gate material layers thatcontain conductive materials (e.g., metal such as tungsten, molybdenum,tantalum, titanium, platinum, ruthenium, and alloys thereof, or a metalsilicide such as tungsten silicide, molybdenum silicide, tantalumsilicide, titanium silicide, nickel silicide, cobalt silicide, or acombination thereof) and/or semiconductor materials (e.g.,polycrystalline or amorphous semiconductor material including at leastone elemental semiconductor element or at least one compoundsemiconductor material). Alternatively or additionally, the chargestorage layer 54 may comprise an insulating charge trapping material,such as one or more silicon nitride segments. Alternatively, the chargestorage layer 54 may comprise conductive nanoparticles such as metalnanoparticles, which can be, for example, ruthenium nanoparticles. Thecharge storage layer 54 can be formed, for example, by chemical vapordeposition (CVD), atomic layer deposition (ALD), physical vapordeposition (PVD), or any suitable deposition technique for storingelectrical charges therein. The thickness of the charge storage layer 54can be in a range from 2 nm to 20 nm, although lesser and greaterthicknesses can also be used.

The tunneling dielectric layer 56 includes a dielectric material throughwhich charge tunneling can be performed under suitable electrical biasconditions. The charge tunneling may be performed through hot-carrierinjection or by Fowler-Nordheim tunneling induced charge transferdepending on the mode of operation of the monolithic three-dimensionalNAND string memory device to be formed. The tunneling dielectric layer56 can include silicon oxide, silicon nitride, silicon oxynitride,dielectric metal oxides (such as aluminum oxide and hafnium oxide),dielectric metal oxynitride, dielectric metal silicates, alloys thereof,and/or combinations thereof. In one embodiment, the tunneling dielectriclayer 56 can include a stack of a first silicon oxide layer, a siliconoxynitride layer, and a second silicon oxide layer, which is commonlyknown as an ONO stack. In one embodiment, the tunneling dielectric layer56 can include a silicon oxide layer that is substantially free ofcarbon or a silicon oxynitride layer that is substantially free ofcarbon. The thickness of the tunneling dielectric layer 56 can be in arange from 2 nm to 20 nm, although lesser and greater thicknesses canalso be used.

The optional first semiconductor channel layer 601 includes asemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the first semiconductor channel layer 601includes amorphous silicon or polysilicon. The first semiconductorchannel layer 601 can be formed by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD). The thickness of thefirst semiconductor channel layer 601 can be in a range from 2 nm to 10nm, although lesser and greater thicknesses can also be used. A memorycavity 49′ is formed in the volume of each memory opening 49 that is notfilled with the deposited material layers (52, 54, 56, 601).

Referring to FIG. 5D, the optional first semiconductor channel layer601, the tunneling dielectric layer 56, the charge storage layer 54, andthe blocking dielectric layer 52 are sequentially anisotropically etchedusing at least one anisotropic etch process. The portions of the firstsemiconductor channel layer 601, the tunneling dielectric layer 56, thecharge storage layer 54, and the blocking dielectric layer 52 locatedabove the top surface of the insulating cap layer 70 can be removed bythe at least one anisotropic etch process. Further, the horizontalportions of the first semiconductor channel layer 601, the tunnelingdielectric layer 56, the charge storage layer 54, and the blockingdielectric layer 52 at a bottom of each memory cavity 49′ can be removedto form openings in remaining portions thereof. Each of the firstsemiconductor channel layer 601, the tunneling dielectric layer 56, thecharge storage layer 54, and the blocking dielectric layer 52 can beetched by a respective anisotropic etch process using a respective etchchemistry, which may, or may not, be the same for the various materiallayers.

Each remaining portion of the first semiconductor channel layer 601 canhave a tubular configuration. The charge storage layer 54 can comprise acharge trapping material or a floating gate material. In one embodiment,each charge storage layer 54 can include a vertical stack of chargestorage regions that store electrical charges upon programming. In oneembodiment, the charge storage layer 54 can be a charge storage layer inwhich each portion adjacent to the sacrificial material layers 42constitutes a charge storage region.

A surface of the pedestal channel portion 11 (or a surface of thesemiconductor material layer 10 in case the pedestal channel portions 11are not used) can be physically exposed underneath the opening throughthe first semiconductor channel layer 601, the tunneling dielectriclayer 56, the charge storage layer 54, and the blocking dielectric layer52. Optionally, the physically exposed semiconductor surface at thebottom of each memory cavity 49′ can be vertically recessed so that therecessed semiconductor surface underneath the memory cavity 49′ isvertically offset from the topmost surface of the pedestal channelportion 11 (or of the semiconductor material layer 10 in case pedestalchannel portions 11 are not used) by a recess distance. A tunnelingdielectric layer 56 is located over the charge storage layer 54. A setof a blocking dielectric layer 52, a charge storage layer 54, and atunneling dielectric layer 56 in a memory opening 49 constitutes amemory film 50, which includes a plurality of charge storage regions(comprising the charge storage layer 54) that are insulated fromsurrounding materials by the blocking dielectric layer 52 and thetunneling dielectric layer 56. In one embodiment, the firstsemiconductor channel layer 601, the tunneling dielectric layer 56, thecharge storage layer 54, and the blocking dielectric layer 52 can havevertically coincident sidewalls.

Referring to FIG. 5E, a second semiconductor channel layer 602 can bedeposited directly on the semiconductor surface of the pedestal channelportion 11 or the semiconductor material layer 10 if the pedestalchannel portion 11 is omitted, and directly on the first semiconductorchannel layer 601. The second semiconductor channel layer 602 includes asemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the second semiconductor channel layer 602includes amorphous silicon or polysilicon. The second semiconductorchannel layer 602 can be formed by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD). The thickness of thesecond semiconductor channel layer 602 can be in a range from 2 nm to 10nm, although lesser and greater thicknesses can also be used. The secondsemiconductor channel layer 602 may partially fill the memory cavity 49′in each memory opening, or may fully fill the cavity in each memoryopening.

The materials of the first semiconductor channel layer 601 and thesecond semiconductor channel layer 602 are collectively referred to as asemiconductor channel material. In other words, the semiconductorchannel material is a set of all semiconductor material in the firstsemiconductor channel layer 601 and the second semiconductor channellayer 602.

Referring to FIG. 5F, in case the memory cavity 49′ in each memoryopening is not completely filled by the second semiconductor channellayer 602, a dielectric core layer 62L can be deposited in the memorycavity 49′ to fill any remaining portion of the memory cavity 49′ withineach memory opening. The dielectric core layer 62L includes a dielectricmaterial such as silicon oxide or organosilicate glass. The dielectriccore layer 62L can be deposited by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD), or by a self-planarizingdeposition process such as spin coating.

Referring to FIG. 5G, the horizontal portion of the dielectric corelayer 62L can be removed, for example, by a recess etch from above thetop surface of the insulating cap layer 70. Each remaining portion ofthe dielectric core layer 62L constitutes a dielectric core 62. Further,the horizontal portion of the second semiconductor channel layer 602located above the top surface of the insulating cap layer 70 can beremoved by a planarization process, which can use a recess etch orchemical mechanical planarization (CMP). Each remaining portion of thesecond semiconductor channel layer 602 can be located entirety within amemory opening 49 or entirely within a support opening 19.

Each adjoining pair of a first semiconductor channel layer 601 and asecond semiconductor channel layer 602 can collectively form a verticalsemiconductor channel 60 through which electrical current can flow whena vertical NAND device including the vertical semiconductor channel 60is turned on. A tunneling dielectric layer 56 is surrounded by a chargestorage layer 54, and laterally surrounds a portion of the verticalsemiconductor channel 60. Each adjoining set of a blocking dielectriclayer 52, a charge storage layer 54, and a tunneling dielectric layer 56collectively constitute a memory film 50, which can store electricalcharges with a macroscopic retention time. In some embodiments, ablocking dielectric layer 52 may not be present in the memory film 50 atthis step, and a blocking dielectric layer may be subsequently formedafter formation of backside recesses. As used herein, a macroscopicretention time refers to a retention time suitable for operation of amemory device as a permanent memory device such as a retention time inexcess of 24 hours.

Referring to FIG. 5H, the top surface of each dielectric core 62 can befurther recessed within each memory opening, for example, by a recessetch to a depth that is located between the top surface of theinsulating cap layer 70 and the bottom surface of the insulating caplayer 70. Drain regions 63 can be formed by depositing a dopedsemiconductor material within each recessed region above the dielectriccores 62. The drain regions 63 can have a doping of a secondconductivity type that is the opposite of the first conductivity type.For example, if the first conductivity type is p-type, the secondconductivity type is n-type, and vice versa. The dopant concentration inthe drain regions 63 can be in a range from 5.0×10¹⁹/cm³ to2.0×10²¹/cm³, although lesser and greater dopant concentrations can alsobe used. The doped semiconductor material can be, for example, dopedpolysilicon. Excess portions of the deposited semiconductor material canbe removed from above the top surface of the insulating cap layer 70,for example, by chemical mechanical planarization (CMP) or a recess etchto form the drain regions 63.

Each combination of a memory film 50 and a vertical semiconductorchannel 60 within a memory opening 49 constitutes a memory stackstructure 55. The memory stack structure 55 is a combination of asemiconductor channel, a tunneling dielectric layer, a plurality ofmemory elements comprising portions of the charge storage layer 54, andan optional blocking dielectric layer 52. Each combination of a pedestalchannel portion 11 (if present), a memory stack structure 55, adielectric core 62, and a drain region 63 within a memory opening 49 isherein referred to as a memory opening fill structure 58. Eachcombination of a pedestal channel portion 11 (if present), a memory film50, a vertical semiconductor channel 60, a dielectric core 62, and adrain region 63 within each support opening 19 fills the respectivesupport openings 19, and constitutes a support pillar structure.

Referring to FIG. 6, the first exemplary structure is illustrated afterformation of memory opening fill structures 58 and support pillarstructure 20 within the memory openings 49 and the support openings 19,respectively. An instance of a memory opening fill structure 58 can beformed within each memory opening 49 of the structure of FIGS. 4A and4B. An instance of the support pillar structure 20 can be formed withineach support opening 19 of the structure of FIGS. 4A and 4B.

Each memory stack structure 55 includes a vertical semiconductor channel60, which may comprise multiple semiconductor channel layers (601, 602),and a memory film 50. The memory film 50 may comprise a tunnelingdielectric layer 56 laterally surrounding the vertical semiconductorchannel 60, a vertical stack of charge storage regions (comprising acharge storage layer 54) laterally surrounding the tunneling dielectriclayer 56, and an optional blocking dielectric layer 52. While thepresent disclosure is described using the illustrated configuration forthe memory stack structure, the methods of the present disclosure can beapplied to alternative memory stack structures including different layerstacks or structures for the memory film 50 and/or for the verticalsemiconductor channel 60.

Each memory stack structure 55 is formed in a respective one of thememory openings 49. As such, the memory stack structures 55 can bearranged in two rows that extend along the first horizontal directionhd1. Memory stack structures 55 within each row have a uniform intra-rowpitch p1. In one embodiment, the memory stack structures 55 can bearranged as a two-dimensional periodic array in which each neighboringpair of rows of memory stack structures 55 has a uniform inter-row pitchp2.

Referring to FIGS. 7A and 7B, a patterned etch mask layer 307 includingelongated openings can be formed over the alternating stack (32, 42) andthe memory stack structures 55. In one embodiment, the patterned etchmask layer 307 can be a patterned photoresist layer formed byapplication and lithographic patterning of a photoresist material overthe alternating stack (32, 42) and the memory stack structures 55. Eachopening in the patterned etch mask layer 307 can overlie a segment ofeach memory stack structure 55 within a neighboring pair of rows ofmemory stack structures 55. Each memory stack structure 55 of which asegment is located within an area of one of the openings in thepatterned etch mask layer 307 is herein referred to as a first memorystack structure 55A. Memory stack structures 55 that are entirelycovered with the patterned etch mask layer 307, for example, by beinglocated between neighboring pairs of first memory stack structures 55A,are herein referred to as a second memory stack structure 55B. Secondmemory stack structures 55B may, or may not, be present in the firstexemplary structure depending on the layout of the elongated openings inthe patterned etch mask layer 307. Each first memory stack structure 55Ais only partly covered with the patterned etch mask layer 307. As such,a first area of each of the first memory stack structures 55A is locatedwithin an area of an elongated opening in the patterned etch mask layer307, and a second area of each of the first memory stack structures 55Bis covered by the patterned etch mask layer 307. The first area can bein a range from 15% to 70%, such as from 25% to 50%, of the entire areaof each first memory stack structure 55A.

Drain regions 63 at an upper end of the first memory stack structures55A are herein referred to as first drain regions 63A, and drain regions63 at an upper end of the second memory stack structures 55B are hereinreferred to as second drain regions 63B. Dielectric cores 62 embeddedwithin the first memory stack structures 55A are herein referred to asfirst dielectric cores 62A, and dielectric cores 62 embedded within thesecond memory stack structures 55B are herein referred to as seconddielectric cores 62B.

An anisotropic etch process is performed to etch an upper portion of thealternating stack (32, 42) and unmasked segments of the first memorystack structures 55A. The unmasked segments of the first memory stackstructures 55A include portions of vertical semiconductor channels 60and the memory films 50 of the first memory stack structures 55A thatare not masked by the patterned etch mask layer 307. Adrain-select-level trench 309 is formed underneath each elongatedopening within the patterned etch mask layer 307 by etching through anupper portion of the alternating stack (32, 42) and a first area of eachof the first memory stack structures 55A. Each drain-select-level trench309 can include a pair of straight lengthwise sidewalls that extendalong the first horizontal direction hd1. The depth of thedrain-select-level trenches 309 can be selected such that thedrain-select-level trenches 309 vertically extend through eachsacrificial material layer located at drain select levels, i.e., levelsin which drain-select-level electrically conductive layers that functionas drain select gate electrodes are to be subsequently formed.

The anisotropic etch process etches portions of memory films 50 andvertical semiconductor channels 60 of the first memory stack structure55A that underlie the elongated opening in the patterned etch mask layer307. A portion of each first drain region 63A can be removed duringformation of the drain-select-level trenches 309. The pair of straightlengthwise sidewalls of each drain-select-level trench 309 can comprisestraight sidewall segments of remaining portions of the first drainregions 63A and straight sidewall segments of the dielectric cores 62.The memory stack structures 55 can comprise second memory stackstructures 55B that are masked with a patterned etch mask layer 307during formation of the drain-select-level trenches 309. Sidewalls ofthe second memory stack structures 55B are not etched during formationof the drain-select-level trenches 309. Thus, each verticalsemiconductor channel 60 of the second memory stack structures 55B has atubular configuration. The patterned etch mask layer 307 can be removed,for example, by ashing after formation of the drain-select-leveltrenches 309.

Referring to FIGS. 8A and 8B, a drain-select-level isolation structure320 can be formed in each drain-select-level trench 309, for example, bydepositing a dielectric material such as silicon oxide in thedrain-select-level trenches 309. Excess portions of the dielectricmaterial can be removed from above the horizontal plane including thetop surface of the insulating cap layer 70 by a planarization process,which can use a recess etch and/or chemical mechanical planarization.Each drain-select-level isolation structure 320 can include a pair ofstraight sidewalls that laterally extend along the first horizontaldirection hd1. Each drain-select-level isolation structure 320 canvertically extend through a plurality of sacrificial material layers 42including a topmost one of the sacrificial material layers 42 within thealternating stack (32, 42). Each vertical semiconductor channel 60within the first memory stack structures 55A comprises a tubular sectionthat underlie a horizontal plane including a bottom surface of adrain-select-level isolation structure 320 and a semi-tubular sectionoverlying the tubular section and contacting the drain-select-levelisolation structure 320. As used herein, a “tubular” element refers toan element that has a shape of a tube. As used herein, a “semi-tubular”element refers to an element having a shape obtained by cutting off asegment of a tubular element to provide two vertically-extendingsidewalls in a remaining portion of the tubular element.

Referring to FIGS. 9A and 9B, a contact level dielectric layer 73 can beformed over the alternating stack (32, 42) of insulating layer 32 andsacrificial material layers 42, and over the memory stack structures 55and the support pillar structures 20. The contact level dielectric layer73 includes a dielectric material that is different from the dielectricmaterial of the sacrificial material layers 42. For example, the contactlevel dielectric layer 73 can include silicon oxide. The contact leveldielectric layer 73 can have a thickness in a range from 50 nm to 500nm, although lesser and greater thicknesses can also be used.

A photoresist layer (not shown) can be applied over the contact leveldielectric layer 73, and is lithographically patterned to form openingsin areas between clusters of memory stack structures 55. The pattern inthe photoresist layer can be transferred through the contact leveldielectric layer 73, the alternating stack (32, 42) and/or theretro-stepped dielectric material portion 65 using an anisotropic etchto form backside trenches 79, which vertically extend from the topsurface of the contact level dielectric layer 73 at least to the topsurface of the substrate (9, 10), and laterally extend through thememory array region 100 and the staircase region 300.

In one embodiment, the backside trenches 79 can laterally extend along afirst horizontal direction hd1 and can be laterally spaced apart amongone another along a second horizontal direction hd2 that isperpendicular to the first horizontal direction hd1. The memory stackstructures 55 can be arranged in rows that extend along the firsthorizontal direction hd1.

The drain-select-level isolation structures 320 can laterally extendalong the first horizontal direction hd1. Each backside trench 79 canhave a uniform width that is invariant along the lengthwise direction(i.e., along the first horizontal direction hd1). Eachdrain-select-level isolation structure 320 can have a uniform verticalcross-sectional profile along vertical planes that are perpendicular tothe first horizontal direction hd1 that is invariant with translationalong the first horizontal direction hd1. Each drain-select-levelisolation structure 320 contacts two rows of first memory stackstructures 55A. In one embodiment, the backside trenches 79 can includea source contact opening in which a source contact via structure can besubsequently formed. The photoresist layer can be removed, for example,by ashing.

Referring to FIGS. 10 and 11A, an etchant that selectively etches thesecond material of the sacrificial material layers 42 with respect tothe first material of the insulating layers 32 can be introduced intothe backside trenches 79, for example, using an etch process. FIG. 9Aillustrates a region of the first exemplary structure of FIG. 8.Backside recesses 43 are formed in volumes from which the sacrificialmaterial layers 42 are removed. The removal of the second material ofthe sacrificial material layers 42 can be selective to the firstmaterial of the insulating layers 32, the material of the retro-steppeddielectric material portion 65, the semiconductor material of thesemiconductor material layer 10, and the material of the outermost layerof the memory films 50. In one embodiment, the sacrificial materiallayers 42 can include silicon nitride, and the materials of theinsulating layers 32 and the retro-stepped dielectric material portion65 can be selected from silicon oxide and dielectric metal oxides.

The etch process that removes the second material selective to the firstmaterial and the outermost layer of the memory films 50 can be a wetetch process using a wet etch solution, or can be a gas phase (dry) etchprocess in which the etchant is introduced in a vapor phase into thebackside trenches 79. For example, if the sacrificial material layers 42include silicon nitride, the etch process can be a wet etch process inwhich the first exemplary structure is immersed within a wet etch tankincluding phosphoric acid, which etches silicon nitride selective tosilicon oxide, silicon, and various other materials used in the art. Thesupport pillar structure 20, the retro-stepped dielectric materialportion 65, and the memory stack structures 55 provide structuralsupport while the backside recesses 43 are present within volumespreviously occupied by the sacrificial material layers 42.

Each backside recess 43 can be a laterally extending cavity having alateral dimension that is greater than the vertical extent of thecavity. In other words, the lateral dimension of each backside recess 43can be greater than the height of the backside recess 43. A plurality ofbackside recesses 43 can be formed in the volumes from which the secondmaterial of the sacrificial material layers 42 is removed. The memoryopenings in which the memory stack structures 55 are formed are hereinreferred to as front side openings or front side cavities in contrastwith the backside recesses 43. In one embodiment, the memory arrayregion 100 comprises an array of monolithic three-dimensional NANDstrings having a plurality of device levels disposed above the substrate(9, 10). In this case, each backside recess 43 can define a space forreceiving a respective word line of the array of monolithicthree-dimensional NAND strings.

Each of the plurality of backside recesses 43 can extend substantiallyparallel to the top surface of the substrate (9, 10). A backside recess43 can be vertically bounded by a top surface of an underlyinginsulating layer 32 and a bottom surface of an overlying insulatinglayer 32. In one embodiment, each backside recess 43 can have a uniformheight throughout.

Physically exposed surface portions of the optional pedestal channelportions 11 and the semiconductor material layer 10 can be convertedinto dielectric material portions by thermal conversion and/or plasmaconversion of the semiconductor materials into dielectric materials. Forexample, thermal conversion and/or plasma conversion can be used toconvert a surface portion of each pedestal channel portion 11 into atubular dielectric spacer 216, and to convert each physically exposedsurface portion of the semiconductor material layer 10 into a planardielectric portion 616. In one embodiment, each tubular dielectricspacer 216 can be topologically homeomorphic to a torus, i.e., generallyring-shaped. As used herein, an element is topologically homeomorphic toa torus if the shape of the element can be continuously stretchedwithout destroying a hole or forming a new hole into the shape of atorus. The tubular dielectric spacers 216 include a dielectric materialthat includes the same semiconductor element as the pedestal channelportions 11 and additionally includes at least one non-metallic elementsuch as oxygen and/or nitrogen such that the material of the tubulardielectric spacers 216 is a dielectric material. In one embodiment, thetubular dielectric spacers 216 can include a dielectric oxide, adielectric nitride, or a dielectric oxynitride of the semiconductormaterial of the pedestal channel portions 11. Likewise, each planardielectric portion 616 includes a dielectric material that includes thesame semiconductor element as the semiconductor material layer andadditionally includes at least one non-metallic element such as oxygenand/or nitrogen such that the material of the planar dielectric portions616 is a dielectric material. In one embodiment, the planar dielectricportions 616 can include a dielectric oxide, a dielectric nitride, or adielectric oxynitride of the semiconductor material of the semiconductormaterial layer 10.

Referring to FIG. 11B, a backside blocking dielectric layer 44 can beoptionally formed. The backside blocking dielectric layer 44, ifpresent, comprises a dielectric material that functions as a controlgate dielectric for the control gates to be subsequently formed in thebackside recesses 43. In case the blocking dielectric layer 52 ispresent within each memory opening, the backside blocking dielectriclayer 44 is optional. In case the blocking dielectric layer 52 isomitted, the backside blocking dielectric layer 44 is present.

The backside blocking dielectric layer 44 can be formed in the backsiderecesses 43 and on a sidewall of the backside trench 79. The backsideblocking dielectric layer 44 can be formed directly on horizontalsurfaces of the insulating layers 32 and sidewalls of the memory stackstructures 55 within the backside recesses 43. If the backside blockingdielectric layer 44 is formed, formation of the tubular dielectricspacers 216 and the planar dielectric portion 616 prior to formation ofthe backside blocking dielectric layer 44 is optional. In oneembodiment, the backside blocking dielectric layer 44 can be formed by aconformal deposition process such as atomic layer deposition (ALD). Thebackside blocking dielectric layer 44 can consist essentially ofaluminum oxide. The thickness of the backside blocking dielectric layer44 can be in a range from 1 nm to 15 nm, such as 2 to 6 nm, althoughlesser and greater thicknesses can also be used.

The dielectric material of the backside blocking dielectric layer 44 canbe a dielectric metal oxide such as aluminum oxide, a dielectric oxideof at least one transition metal element, a dielectric oxide of at leastone Lanthanide element, a dielectric oxide of a combination of aluminum,at least one transition metal element, and/or at least one Lanthanideelement. Alternatively or additionally, the backside blocking dielectriclayer 44 can include a silicon oxide layer. The backside blockingdielectric layer 44 can be deposited by a conformal deposition methodsuch as chemical vapor deposition or atomic layer deposition. Thebackside blocking dielectric layer 44 is formed on the sidewalls of thebackside trenches 79, horizontal surfaces and sidewalls of theinsulating layers 32, the portions of the sidewall surfaces of thememory stack structures 55 that are physically exposed to the backsiderecesses 43, and a top surface of the planar dielectric portion 616. Abackside cavity 79′ is present within the portion of each backsidetrench 79 that is not filled with the backside blocking dielectric layer44.

Referring to FIG. 11C, a metallic barrier layer 46A can be deposited inthe backside recesses 43. The metallic barrier layer 46A includes anelectrically conductive metallic material that can function as adiffusion barrier layer and/or adhesion promotion layer for a metallicfill material to be subsequently deposited. The metallic barrier layer46A can include a conductive metallic nitride material such as TiN, TaN,WN, or a stack thereof, or can include a conductive metallic carbidematerial such as TiC, TaC, WC, or a stack thereof. In one embodiment,the metallic barrier layer 46A can be deposited by a conformaldeposition process such as chemical vapor deposition (CVD) or atomiclayer deposition (ALD). The thickness of the metallic barrier layer 46Acan be in a range from 2 nm to 8 nm, such as from 3 nm to 6 nm, althoughlesser and greater thicknesses can also be used. In one embodiment, themetallic barrier layer 46A can consist essentially of a conductive metalnitride such as TiN.

Referring to FIGS. 11D and 12, a metal fill material is deposited in theplurality of backside recesses 43, on the sidewalls of the at least onethe backside trench 79, and over the top surface of the contact leveldielectric layer 73 to form a metallic fill material layer 46B. Themetallic fill material can be deposited by a conformal depositionmethod, which can be, for example, chemical vapor deposition (CVD),atomic layer deposition (ALD), electroless plating, electroplating, or acombination thereof. In one embodiment, the metallic fill material layer46B can consist essentially of at least one elemental metal. The atleast one elemental metal of the metallic fill material layer 46B can beselected, for example, from tungsten, cobalt, ruthenium, titanium, andtantalum. In one embodiment, the metallic fill material layer 46B canconsist essentially of a single elemental metal. In one embodiment, themetallic fill material layer 46B can be deposited using afluorine-containing precursor gas such as WF₆. In one embodiment, themetallic fill material layer 46B can be a tungsten layer including aresidual level of fluorine atoms as impurities. The metallic fillmaterial layer 46B is spaced from the insulating layers 32 and thememory stack structures 55 by the metallic barrier layer 46A, which is ametallic barrier layer that blocks diffusion of fluorine atomstherethrough.

A plurality of electrically conductive layers 46 can be formed in theplurality of backside recesses 43, and a continuous electricallyconductive material layer 46L can be formed on the sidewalls of eachbackside trench 79 and over the contact level dielectric layer 73. Eachelectrically conductive layer 46 includes a portion of the metallicbarrier layer 46A and a portion of the metallic fill material layer 46Bthat are located between a vertically neighboring pair of dielectricmaterial layers such as a pair of insulating layers 32. The continuouselectrically conductive material layer 46L includes a continuous portionof the metallic barrier layer 46A and a continuous portion of themetallic fill material layer 46B that are located in the backsidetrenches 79 or above the contact level dielectric layer 73.

Each sacrificial material layer 42 can be replaced with an electricallyconductive layer 46. A backside cavity 79′ is present in the portion ofeach backside trench 79 that is not filled with the backside blockingdielectric layer 44 and the continuous electrically conductive materiallayer 46L. A tubular dielectric spacer 216 laterally surrounds apedestal channel portion 11. A bottommost electrically conductive layer46 laterally surrounds each tubular dielectric spacer 216 upon formationof the electrically conductive layers 46.

Referring to FIG. 13, the deposited metallic material of the continuouselectrically conductive material layer 46L is etched back from thesidewalls of each backside trench 79 and from above the contact leveldielectric layer 73, for example, by an isotropic wet etch, ananisotropic dry etch, or a combination thereof. Each remaining portionof the deposited metallic material in the backside recesses 43constitutes an electrically conductive layer 46. Each electricallyconductive layer 46 can be a conductive line structure. Thus, thesacrificial material layers 42 are replaced with the electricallyconductive layers 46.

Each electrically conductive layer 46 can function as a combination of aplurality of control gate electrodes located at a same level and a wordline electrically interconnecting, i.e., electrically connecting, theplurality of control gate electrodes located at the same level. Theplurality of control gate electrodes within each electrically conductivelayer 46 are the control gate electrodes for the vertical memory devicesincluding the memory stack structures 55. In other words, eachelectrically conductive layer 46 can be a word line that functions as acommon control gate electrode for the plurality of vertical memorydevices.

In one embodiment, the removal of the continuous electrically conductivematerial layer 46L can be selective to the material of the backsideblocking dielectric layer 44. In this case, a horizontal portion of thebackside blocking dielectric layer 44 can be present at the bottom ofeach backside trench 79. In another embodiment, the removal of thecontinuous electrically conductive material layer 46L may not beselective to the material of the backside blocking dielectric layer 44or, the backside blocking dielectric layer 44 may not be used. Theplanar dielectric portions 616 can be removed during removal of thecontinuous electrically conductive material layer 46L. A backside cavity79′ is present within each backside trench 79.

Referring to FIGS. 14A and 14B, an insulating material layer can beformed in the backside trenches 79 and over the contact level dielectriclayer 73 by a conformal deposition process. Exemplary conformaldeposition processes include, but are not limited to, chemical vapordeposition and atomic layer deposition. The insulating material layerincludes an insulating material such as silicon oxide, silicon nitride,a dielectric metal oxide, an organosilicate glass, or a combinationthereof. In one embodiment, the insulating material layer can includesilicon oxide. The insulating material layer can be formed, for example,by low pressure chemical vapor deposition (LPCVD) or atomic layerdeposition (ALD). The thickness of the insulating material layer can bein a range from 1.5 nm to 60 nm, although lesser and greater thicknessescan also be used.

If a backside blocking dielectric layer 44 is present, the insulatingmaterial layer can be formed directly on surfaces of the backsideblocking dielectric layer 44 and directly on the sidewalls of theelectrically conductive layers 46. If a backside blocking dielectriclayer 44 is not used, the insulating material layer can be formeddirectly on sidewalls of the insulating layers 32 and directly onsidewalls of the electrically conductive layers 46.

An anisotropic etch is performed to remove horizontal portions of theinsulating material layer from above the contact level dielectric layer73 and at the bottom of each backside trench 79. Each remaining portionof the insulating material layer constitutes an insulating spacer 74. Abackside cavity 79′ is present within a volume surrounded by eachinsulating spacer 74. A top surface of the semiconductor material layer10 can be physically exposed at the bottom of each backside trench 79.

A source region 61 can be formed at a surface portion of thesemiconductor material layer 10 under each backside cavity 79′ byimplantation of electrical dopants into physically exposed surfaceportions of the semiconductor material layer 10. Each source region 61is formed in a surface portion of the substrate (9, 10) that underlies arespective opening through the insulating spacer 74. Due to the straggleof the implanted dopant atoms during the implantation process andlateral diffusion of the implanted dopant atoms during a subsequentactivation anneal process, each source region 61 can have a lateralextent greater than the lateral extent of the opening through theinsulating spacer 74.

In one embodiment, the substrate (9, 10) includes the semiconductormaterial layer 10, and the semiconductor material layer 10 and the firstvertical semiconductor channels 60 of the first memory stack structures55A have a doping of a first conductivity type. Pedestal channelportions 11 are disposed between bottom ends of the first verticalsemiconductor channels 60 and the substrate semiconductor layer 9, and asource region 61 having a doping of a second conductivity type isembedded within the semiconductor material layer 10 and is laterallyspaced from the first memory stack structures 55A and the pedestalchannel portions 11.

An upper portion of the semiconductor material layer 10 that extendsbetween the source region 61 and the plurality of pedestal channelportions 11 constitutes a horizontal semiconductor channel 59 for aplurality of field effect transistors. The horizontal semiconductorchannel 59 is connected to multiple vertical semiconductor channels 60through respective pedestal channel portions 11. The horizontalsemiconductor channel 59 contacts the source region 61 and the pluralityof pedestal channel portions 11. A bottommost electrically conductivelayer 46 provided upon formation of the electrically conductive layers46 within the alternating stack (32, 46) can comprise a select gateelectrode for the field effect transistors. Each source region 61 isformed in an upper portion of the substrate (9, 10). Semiconductorchannels (59, 11, 60) extend between each source region 61 and arespective set of drain regions 63. The semiconductor channels (59, 11,60) include the vertical semiconductor channels 60 of the memory stackstructures 55.

A backside contact via structure 76 can be formed within each backsidecavity 79′. Each contact via structure 76 can fill a respective backsidecavity 79′. The contact via structures 76 can be formed by depositing atleast one conductive material in the remaining unfilled volume (i.e.,the backside cavity 79′) of the backside trench 79. For example, the atleast one conductive material can include a conductive liner 76A and aconductive fill material portion 76B. The conductive liner 76A caninclude a conductive metallic liner such as TiN, TaN, WN, TiC, TaC, WC,an alloy thereof, or a stack thereof. The thickness of the conductiveliner 76A can be in a range from 3 nm to 30 nm, although lesser andgreater thicknesses can also be used. The conductive fill materialportion 76B can include a metal or a metallic alloy. For example, theconductive fill material portion 76B can include W, Cu, Al, Co, Ru, Ni,an alloy thereof, or a stack thereof.

The at least one conductive material can be planarized using the contactlevel dielectric layer 73 overlying the alternating stack (32, 46) as astopping layer. If chemical mechanical planarization (CMP) process isused, the contact level dielectric layer 73 can be used as a CMPstopping layer. Each remaining continuous portion of the at least oneconductive material in the backside trenches 79 constitutes a backsidecontact via structure 76.

The backside contact via structure 76 extends through the alternatingstack (32, 46), and contacts a top surface of the source region 61. If abackside blocking dielectric layer 44 is used, the backside contact viastructure 76 can contact a sidewall of the backside blocking dielectriclayer 44.

Referring to FIGS. 15A and 15B, additional contact via structures (88,86) can be formed through the contact level dielectric layer 73, andoptionally through the retro-stepped dielectric material portion 65. Forexample, drain contact via structures 88 can be formed through thecontact level dielectric layer 73 on each drain region 63. Word linecontact via structures 86 can be formed on the electrically conductivelayers 46 through the contact level dielectric layer 73, and through theretro-stepped dielectric material portion 65. Peripheral device contactvia structures (not shown) can be formed through the retro-steppeddielectric material portion 65 directly on respective nodes of theperipheral devices.

Each drain contact via structure 88 contacts a top surface of anunderlying one of the drain regions 63. Drain contact via structures 88that contact first drain regions 63A can contact a sidewall of arespective one of the first drain regions 63A. Drain contact viastructure that contact second drain regions 63B can contact only a topsurface of a respective one of the second drain regions 63B.

Referring to FIG. 16, memory-side dielectric material layers 960 can bedeposited over the contact level dielectric layer 73. Variousmemory-side metal interconnect structures 980 can be formed in thememory-side dielectric material layers 960. The memory-side metalinterconnect structures 980 can include bit lines 98 that overlie thememory stack structures 55 and electrically connected to a respectivesubset of the drain regions 63. Further, the memory-side metalinterconnect structures 980 can include additional metal via structuresand additional metal line structures that provide electrical wiringamong the various underlying elements such as the backside contact viastructures 76, the word line contact via structures 86, the bit lines98, and other nodes of the three-dimensional memory device that may beformed as needed. The thickness of the memory-side dielectric materiallayers 960 may be in a range from 300 nm to 3,000 nm, although lesserand greater thicknesses can also be used.

Pad cavities are formed in the upper portion of the memory-side metalinterconnect structures 980 such that a respective one of thememory-side metal interconnect structures 980 is exposed at the bottomof each pad cavity. In one embodiment, the pad cavities can be arrangedas a one-dimensional array or as a two-dimensional array, and may have arespective polygonal, circular, elliptical, or generally-curvilinearshape. A conductive material can be deposited in the pad cavities toform various memory-side bonding pads 988. The memory-side bonding pads988 are embedded in memory-side dielectric material layers 960, which isformed over the alternating stack (32, 46). The memory-side bonding pads988 are electrically connected to nodes of the memory stack structures55. In one embodiment, each bit line 98 can be electrically connected toa respective one of the memory-side bonding pads 988. The firstexemplary structure comprises a memory die 900.

In case the at least one semiconductor device 700 in the peripheraldevice region 200 includes a peripheral circuitry for controllingoperation of memory stack structures 55 in the three-dimensional arrayof memory elements, the memory stack structure 55, the electricallyconductive layers 46 that function as word lines, and the bit lines 98of the three-dimensional memory device can be controlled by theperipheral circuitry of the memory die 900. Alternatively oradditionally, a support die (not shown) can be used to control variousnodes of the three-dimensional memory device. In this case, the supportdie can include a peripheral circuitry for controlling operation ofmemory stack structures 55 in the three-dimensional array of memoryelements, the memory stack structure 55, the electrically conductivelayers 46 that function as word lines, and the bit lines 98 of thethree-dimensional memory device. The support die can be bonded to thememory die 900 using the memory-side bonding pads 988.

Referring to FIG. 17, a second exemplary structure according to a secondembodiment of the present disclosure is illustrated, which can bederived from the first exemplary structure of FIG. 6. A sacrificialplanarization stopper layer 373 can be formed over the insulating caplayer 70 after the processing steps of FIG. 6. The sacrificialplanarization stopper layer 373 includes a material that can be used asa planarization stopper structure and is different from the material ofthe sacrificial material layers 42. In one embodiment, the sacrificialplanarization stopper layer 373 can include the same material as thecontact level dielectric layer 73. Subsequently, backside trenches 79are formed through the sacrificial planarization stopper layer 373 andthe alternating stack (32, 42) by performing the processing steps ofFIGS. 9A and 9B. Subsequently, the processing steps of FIGS. 10,11A-11D, 12, 13, and 14A and 14B can be performed to provide the secondexemplary structure illustrated in FIG. 17.

Referring to FIG. 18, portions of the second exemplary structure locatedabove the horizontal plane including the top surface of the insulatingcap layer 70 can be removed by performing at least one planarizationprocess. The sacrificial planarization stopper layer 373 and portions ofthe insulating spacers 74 and the backside contact via structures 76that protrude above the horizontal plane including the top surface ofthe insulating cap layer 70 by chemical mechanical planarization and/orat least one recess etch process.

Referring to FIGS. 19A and 19B, a patterned etch mask layer 317including elongated openings can be formed over the alternating stack(32, 46) and the memory stack structures 55. In one embodiment, thepatterned etch mask layer 317 can be a patterned photoresist layerformed by application and lithographic patterning of a photoresistmaterial over the alternating stack (32, 46) and the memory stackstructures 55. Each opening in the patterned etch mask layer 317 canoverlie a segment of each memory stack structure 55 within a neighboringpair of rows of memory stack structures 55. Each memory stack structure55 of which a segment is located within an area of one of the openingsin the patterned etch mask layer 317 is herein referred to as a firstmemory stack structure 55A. Memory stack structures 55 that are entirelycovered with the patterned etch mask layer 317, for example, by beinglocated between neighboring pairs of first memory stack structures 55A,are herein referred to as a second memory stack structure 55B. Secondmemory stack structures 55B may, or may not, be present in the firstexemplary structure depending on the layout of the elongated openings inthe patterned etch mask layer 317. Each first memory stack structure 55Ais only partly covered with the patterned etch mask layer 317. As such,a first area of each of the first memory stack structures 55A is locatedwithin an area of an elongated opening in the patterned etch mask layer317, and a second area of each of the first memory stack structures 55Bis covered by the patterned etch mask layer 317. The first area can bein a range from 15% to 70%, such as from 25% to 50%, of the entire areaof each first memory stack structure 55A.

Drain regions 63 at an upper end of the first memory stack structures55A are herein referred to as first drain regions 63A, and drain regions63 at an upper end of the second memory stack structures 55B are hereinreferred to as second drain regions 63B. Dielectric cores 62 embeddedwithin the first memory stack structures 55A are herein referred to asfirst dielectric cores 62A, and dielectric cores 62 embedded within thesecond memory stack structures 55B are herein referred to as seconddielectric cores 62B.

Referring to FIG. 20, an anisotropic etch process is performed to etchan upper portion of the alternating stack (32, 46) and unmasked segmentsof the first memory stack structures 55A. The unmasked segments of thefirst memory stack structures 55A include portions of verticalsemiconductor channels 60 and the memory films 50 of the first memorystack structures 55A that are not masked by the patterned etch masklayer 317. A drain-select-level trench 309 is formed underneath eachelongated opening within the patterned etch mask layer 317 by etchingthrough an upper portion of the alternating stack (32, 46) and a firstarea of each of the first memory stack structures 55A. Eachdrain-select-level trench 309 can include a pair of straight lengthwisesidewalls that extend along the first horizontal direction hd1. Thedepth of the drain-select-level trenches 309 can be selected such thatthe drain-select-level trenches 309 vertically extend through eachsacrificial material layer located at drain select levels, i.e., levelsin which drain-select-level electrically conductive layers that functionas drain select gate electrodes are to be subsequently formed.

The anisotropic etch process etches portions of memory films 50 andvertical semiconductor channels 60 of the first memory stack structure55A that underlie the elongated opening in the patterned etch mask layer317. A portion of each first drain region 63A can be removed duringformation of the drain-select-level trenches 309. The pair of straightlengthwise sidewalls of each drain-select-level trench 309 can comprisestraight sidewall segments of remaining portions of the first drainregions 63A. The memory stack structures 55 can comprise second memorystack structures 55B that are masked with a patterned etch mask layer317 during formation of the drain-select-level trenches 309. Sidewallsof the second memory stack structures 55B are not etched duringformation of the drain-select-level trenches 309. Thus, each verticalsemiconductor channel 60 of the second memory stack structures 55B has atubular configuration. The patterned etch mask layer 317 can be removed,for example, by ashing after formation of the drain-select-leveltrenches 309.

Referring to FIG. 21, a drain-select-level isolation structure 320 canbe formed in each drain-select-level trench 309, for example, bydepositing a dielectric material such as silicon oxide in thedrain-select-level trenches 309. Excess portions of the dielectricmaterial can be removed from above the horizontal plane including thetop surface of the insulating cap layer 70 by a planarization process,which can use a recess etch and/or chemical mechanical planarization.Each drain-select-level isolation structure 320 can include a pair ofstraight sidewalls that laterally extend along the first horizontaldirection hd1. Each drain-select-level isolation structure 320 canvertically extend through a plurality of electrically conductive layers46 including a topmost one of the electrically conductive layers withinthe alternating stack (32, 46). Each vertical semiconductor channel 60within the first memory stack structures 55A comprises a tubular sectionthat underlie a horizontal plane including a bottom surface of adrain-select-level isolation structure 320 and a semi-tubular sectionoverlying the tubular section and contacting the drain-select-levelisolation structure 320.

Continuing to refer to FIG. 21, a contact level dielectric layer 73 canbe formed over the alternating stack (32, 46) of insulating layer 32 andelectrically conductive layers 46, and over the memory stack structures55 and the support pillar structures 20. The contact level dielectriclayer 73 includes a dielectric material that is different from thedielectric material of the sacrificial material layers 42. For example,the contact level dielectric layer 73 can include silicon oxide. Thecontact level dielectric layer 73 can have a thickness in a range from50 nm to 500 nm, although lesser and greater thicknesses can also beused.

Referring to FIGS. 22A and 22B, the processing steps of FIGS. 15A and15B can be performed to form additional contact via structures (88, 86)through the contact level dielectric layer 73, and optionally throughthe retro-stepped dielectric material portion 65. For example, draincontact via structures 88 can be formed through the contact leveldielectric layer 73 on each drain region 63. Word line contact viastructures 86 can be formed on the electrically conductive layers 46through the contact level dielectric layer 73, and through theretro-stepped dielectric material portion 65. Peripheral device contactvia structures (not shown) can be formed through the retro-steppeddielectric material portion 65 directly on respective nodes of theperipheral devices.

Each drain contact via structure 88 contacts a top surface of anunderlying one of the drain regions 63. Drain contact via structures 88that contact first drain regions 63A can contact a sidewall of arespective one of the first drain regions 63A. Drain contact viastructure that contact second drain regions 63B can contact only a topsurface of a respective one of the second drain regions 63B.

Referring to FIG. 23, an alternative embodiment of the second exemplarystructure according to the second embodiment of the present disclosureis illustrated, which can be derived from the second exemplary structureof FIG. 18 by forming a patterned etch mask layer 317 having the samepattern as the patterned etch mask layer of FIGS. 19A and 19B, and byperforming an anisotropic etch process with a different etch chemistrythan the anisotropic etch process of FIGS. 19A and 19B. Specifically,the etch chemistry of the anisotropic etch process can be selected suchthat the anisotropic etch process etches unmasked portions of theinsulating cap layer 70, the insulating layers 32, the electricallyconductive layers 46, the drain regions 63, and the dielectric cores 62selective to at least one material of the memory films 50. For example,the charge storage layers 54 can include silicon nitride, and theanisotropic etch process can have an etch chemistry that is selective tosilicon nitride. In this case, unetched portions of the memory films 50can protrude inside each drain-select-level trench 309.

Referring to FIG. 24, portions of memory films 50 of the first memorystack structures 55A that underlie the elongated opening in thepatterned etch mask layer 317 can be removed by performing an isotropicetch process after performing the anisotropic etch process at theprocessing steps of FIG. 23. Protruding portions of the memory films 50inside the drain-select-level trenches 309 are removed during isotropicetch process. The etch chemistry of the isotropic etch process can beselected to etch the material(s) of the protruding portions of thememory films 50. For example, a wet etch process using a combination ofhydrofluoric acid and ethylene glycol can be used to isotropically etchthe protruding portions of the memory films 50. The patterned etch masklayer 317 can be subsequently removed, for example, by ashing. Theresulting structure can be substantially the same as the secondexemplary structure of FIG. 20 after removal of the patterned etch masklayer 317. The processing steps of FIGS. 21, 22A, and 22B can besubsequently performed to provide the second exemplary structureillustrated in FIGS. 22A and 22B.

Referring to FIGS. 25A and 25B, a third exemplary structure according toa third embodiment of the present disclosure can be derived from thefirst exemplary structure of FIG. 1 by forming a layer stack including adielectric isolation layer 768, an optional conductive plate layer 6,and in-process source-level material layers 310′ in lieu of thesemiconductor material layer 10. The dielectric isolation layer 768electrically isolates the in-process source-level material layers 310′from the substrate semiconductor layer 9. The optional conductive platelayer 6, if present, provides a high conductivity conduction path forelectrical current that flows into, or out of, the in-processsource-level material layers 310′.

The optional conductive plate layer 6 includes a conductive materialsuch as a metal or a heavily doped semiconductor material. The optionalconductive plate layer 6, for example, may include a tungsten layerhaving a thickness in a range from 3 nm to 100 nm, although lesser andgreater thicknesses may also be used. A metal nitride layer (not shown)may be provided as a diffusion barrier layer on top of the conductiveplate layer 6. The conductive plate layer 6 may function as a specialsource line in the completed device. In addition, the conductive platelayer 6 may comprise an etch stop layer and may comprise any suitableconductive, semiconductor or insulating layer. The optional conductiveplate layer 6 may include a metallic compound material such as aconductive metallic nitride (e.g., TiN) and/or a metal (e.g., W). Thethickness of the optional conductive plate layer 6 may be in a rangefrom 5 nm to 100 nm, although lesser and greater thicknesses may also beused.

The in-process source-level material layers 310′ may include variouslayers that are subsequently modified to form source-level materiallayers. The source-level material layers, upon formation, include asource contact layer that functions as a common source region forvertical field effect transistors of a three-dimensional memory device.In one embodiment, the in-process source-level material layers 310′ mayinclude, from bottom to top, a lower source-level semiconductor layer112, a lower sacrificial liner 103, a source-level sacrificial layer104, an upper sacrificial liner 105, an upper source-level semiconductorlayer 116, a source-level insulating layer 117, and an optionalsource-select-level conductive layer 118.

The lower source-level semiconductor layer 112 and the uppersource-level semiconductor layer 116 may include a doped semiconductormaterial such as doped polysilicon or doped amorphous silicon. Theconductivity type of the lower source-level semiconductor layer 112 andthe upper source-level semiconductor layer 116 may be the opposite ofthe conductivity of vertical semiconductor channels to be subsequentlyformed. For example, if the vertical semiconductor channels to besubsequently formed have a doping of a first conductivity type, thelower source-level semiconductor layer 112 and the upper source-levelsemiconductor layer 116 have a doping of a second conductivity type thatis the opposite of the first conductivity type. The thickness of each ofthe lower source-level semiconductor layer 112 and the uppersource-level semiconductor layer 116 may be in a range from 10 nm to 300nm, such as from 20 nm to 150 nm, although lesser and greaterthicknesses may also be used.

The source-level sacrificial layer 104 includes a sacrificial materialthat may be removed selective to the lower sacrificial liner 103 and theupper sacrificial liner 105. In one embodiment, the source-levelsacrificial layer 104 may include a semiconductor material such asundoped amorphous silicon or a silicon-germanium alloy with an atomicconcentration of germanium greater than 20%. The thickness of thesource-level sacrificial layer 104 may be in a range from 30 nm to 400nm, such as from 60 nm to 200 nm, although lesser and greaterthicknesses may also be used.

The lower sacrificial liner 103 and the upper sacrificial liner 105include materials that may function as an etch stop material duringremoval of the source-level sacrificial layer 104. For example, thelower sacrificial liner 103 and the upper sacrificial liner 105 mayinclude silicon oxide, silicon nitride, and/or a dielectric metal oxide.In one embodiment, each of the lower sacrificial liner 103 and the uppersacrificial liner 105 may include a silicon oxide layer having athickness in a range from 2 nm to 30 nm, although lesser and greaterthicknesses may also be used.

The source-level insulating layer 117 includes a dielectric materialsuch as silicon oxide. The thickness of the source-level insulatinglayer 117 may be in a range from 20 nm to 400 nm, such as from 40 nm to200 nm, although lesser and greater thicknesses may also be used. Theoptional source-select-level conductive layer 118 may include aconductive material that may be used as a source-select-level gateelectrode. For example, the optional source-select-level conductivelayer 118 may include a doped semiconductor material such as dopedpolysilicon or doped amorphous silicon that may be subsequentlyconverted into doped polysilicon by an anneal process. The thickness ofthe optional source-select-level conductive layer 118 may be in a rangefrom 30 nm to 200 nm, such as from 60 nm to 100 nm, although lesser andgreater thicknesses may also be used.

The in-process source-level material layers 310′ may be formed directlyabove a subset of the semiconductor devices on the substrate (such asthe substrate semiconductor layer 9). As used herein, a first element islocated “directly above” a second element if the first element islocated above a horizontal plane including a topmost surface of thesecond element and an area of the first element and an area of thesecond element has an areal overlap in a plan view (i.e., along avertical plane or direction perpendicular to the top surface of thesubstrate.

The optional conductive plate layer 6 and the in-process source-levelmaterial layers 310′ may be patterned to provide openings in areas inwhich through-memory-level contact via structures and through-dielectriccontact via structures are to be subsequently formed. Patterned portionsof the stack of the conductive plate layer 6 and the in-processsource-level material layers 310′ are present in each memory arrayregion 100 in which three-dimensional memory stack structures are to besubsequently formed.

Subsequently, the processing steps of FIG. 2 can be performed with amodification such that the topmost sacrificial material layer 42 isreplaced with a drain-select-level sacrificial material layer 342, andthe insulating cap layer 70 is replaced with a sacrificial insulatingcap layer 370 that is subsequently removed. In one embodiment, thedrain-select-level sacrificial material layer 342 can have a thicknessin a range from 1.0 times the average thickness of the sacrificialmaterial layers 42 to 10 time the average thickness of the sacrificialmaterial layers 42, such as from 2 times the average thickness of thesacrificial material layers 42 to 6 time the average thickness of thesacrificial material layers 42, although lesser and greater thicknessescan also be used. In one embodiment, the drain-select-level sacrificialmaterial layer 342 can include the same material as the sacrificialmaterial layers 42. The sacrificial insulating cap layer 370 can includethe same material as the insulating cap layer 70 of the firstembodiment.

Subsequently, the processing steps of FIG. 3 can be performed to formstepped surfaces in the staircase region 300. A retro-stepped dielectricmaterial portion 65 can be formed over the stepped surfaces of thestaircase region 300 by deposition and planarization of a dielectricmaterial.

Referring to FIGS. 26A and 26B, the processing steps of FIGS. 4A and 4Bcan be performed to form memory openings 49 and support openings 19. Thelayout of the memory openings 49 and the support openings may be thesame as in the first embodiment. The chemistry of the anisotropic etchprocess may be selected such that each memory opening 49 extends throughthe optional source-select-level conductive layer 118, the source-levelinsulating layer 117, the upper source-level semiconductor layer 116,the source-level sacrificial layer 104, and the lower sacrificial liner103, and into an upper portion of the lower source-level semiconductorlayer 112.

Referring to FIG. 27, a stack of layers including a blocking dielectriclayer 52, a charge storage layer 54, a tunneling dielectric layer 56,and a semiconductor channel material layer may be sequentially depositedin each of the memory openings 49 and the support openings 19. Each ofthe blocking dielectric layer 52, the charge storage layer 54, and thetunneling dielectric layer 56 may have the same composition and the samethickness as in the first embodiment. The semiconductor channel materiallayer can have the same thickness and the same composition as thevertical semiconductor channel 60 of the first embodiment. A dielectricmaterial is deposited in unfilled cavities in the memory openings 49 andin the support openings 19, and is vertically recessed to formdielectric cores 62. Excess portions of the blocking dielectric layer52, the charge storage layer 54, and the tunneling dielectric layer 56,the semiconductor channel material layer are removed from outside thememory openings 49 and the support openings 19. Each remaining portionof the semiconductor channel material layer in a memory opening 49 or ina support opening 19 constitutes a vertical semiconductor channel 60. Asemiconductor material having a doping of a second conductivity type canbe deposited in recesses above the dielectric cores 62 to form drainregions 63.

Referring to FIGS. 28A and 28B, a patterned etch mask layer 307including elongated openings can be formed over the alternating stack(32, 42) and the memory stack structures 55. In one embodiment, thepatterned etch mask layer 307 can be a patterned photoresist layerformed by application and lithographic patterning of a photoresistmaterial over the alternating stack (32, 42) and the memory stackstructures 55. Each opening in the patterned etch mask layer 307 canoverlie a segment of each memory stack structure 55 within a neighboringpair of rows of memory stack structures 55. An opening in the patternedetch mask layer 307 is provided in each area in which backside trenchesare to be subsequently formed. Each row of memory stack structures 55that are most proximal to an area in which a backside trench is to besubsequently formed is partly exposed underneath one of the openings inthe patterned etch mask layer 307.

Each memory stack structure 55 of which a segment is located within anarea of one of the openings in the patterned etch mask layer 307 isherein referred to as a first memory stack structure 55A. Memory stackstructures 55 that are entirely covered with the patterned etch masklayer 307, for example, by being located between neighboring pairs offirst memory stack structures 55A, are herein referred to as a secondmemory stack structure 55B. Second memory stack structures 55B may, ormay not, be present in the first exemplary structure depending on thelayout of the elongated openings in the patterned etch mask layer 307.Each first memory stack structure 55A is only partly covered with thepatterned etch mask layer 307. As such, a first area of each of thefirst memory stack structures 55A is located within an area of anelongated opening in the patterned etch mask layer 307, and a secondarea of each of the first memory stack structures 55B is covered by thepatterned etch mask layer 307. The first area can be in a range from 15%to 70%, such as from 25% to 50%, of the entire area of each first memorystack structure 55A. Each row of memory stack structures 55 thatneighbors an area in which a backside trench is to be subsequentlyformed is a row of first memory stack structures 55A.

Drain regions 63 at an upper end of the first memory stack structures55A are herein referred to as first drain regions 63A, and drain regions63 at an upper end of the second memory stack structures 55B are hereinreferred to as second drain regions 63B. Dielectric cores 62 embeddedwithin the first memory stack structures 55A are herein referred to asfirst dielectric cores 62A, and dielectric cores 62 embedded within thesecond memory stack structures 55B are herein referred to as seconddielectric cores 62B. Each vertical semiconductor channel 60A of thefirst memory stack structures 55A is herein referred to as a firstvertical semiconductor channel 60, and each vertical semiconductorchannel 60 of the second memory stack structures 55B is herein referredto as a second vertical semiconductor channel 60B. Each memory film 50of the first memory stack structures 55A is herein referred to as afirst memory film 50A, and each memory film 50 of the second memorystack structures 55B is herein referred to as a second memory film 50B.

An anisotropic etch process is performed to etch unmasked portions ofthe sacrificial insulating cap layer 370 and the drain-select-levelsacrificial material layer 342 and unmasked segments of the first memorystack structures 55A. The unmasked segments of the first memory stackstructures 55A include portions of vertical semiconductor channels (60A,60B) and the memory films (50A, 50B) of the first memory stackstructures 55A that are not masked by the patterned etch mask layer 307.A drain-select-level trench 309 is formed underneath each elongatedopening within the patterned etch mask layer 307 by etching throughunmasked portions of the sacrificial insulating cap layer 370 and thedrain-select-level sacrificial material layer 342 and a first area ofeach of the first memory stack structures 55A (i.e., unmasked portionsof the first memory stack structures 55A). Each drain-select-leveltrench 309 can include a pair of straight lengthwise sidewalls thatextend along the first horizontal direction hd1. The depth of thedrain-select-level trenches 309 can be selected such that thedrain-select-level trenches 309 vertically extend through thesacrificial insulating cap layer 370 and the drain-select-levelsacrificial material layer 342, and does not extend into sacrificialmaterial layers 42.

The anisotropic etch process etches portions of memory films (50A, 50B)of the first memory stack structure 55A that underlie the elongatedopening in the patterned etch mask layer 307. A portion of each firstdrain region 63A can be removed during formation of thedrain-select-level trenches 309. The pair of straight lengthwisesidewalls of each drain-select-level trench 309 can comprise straightsidewall segments of remaining portions of the first drain regions 63Aand straight sidewall segments of the dielectric cores (62A, 62B). Thememory stack structures (55A, 55B) can comprise second memory stackstructures 55B that are masked with a patterned etch mask layer 307during formation of the drain-select-level trenches 309. Sidewalls ofthe second memory stack structures 55B are not etched during formationof the drain-select-level trenches 309. Thus, each verticalsemiconductor channel (60A, 60B) of the second memory stack structures55B has a tubular configuration. The patterned etch mask layer 307 canbe removed, for example, by ashing after formation of thedrain-select-level trenches 309.

Referring to FIGS. 29A and 29B, a drain-select-level isolation structure320 can be formed in each drain-select-level trench 309, for example, bydepositing a dielectric material such as silicon oxide in thedrain-select-level trenches 309. Excess portions of the dielectricmaterial can be removed from above the horizontal plane including thetop surface of the sacrificial insulating cap layer 370 by aplanarization process, which can use a recess etch and/or chemicalmechanical planarization. Each drain-select-level isolation structure320 can include a pair of straight sidewalls that laterally extend alongthe first horizontal direction hd1. Each drain-select-level isolationstructure 320 can vertically extend through the drain-select-levelsacrificial material layer 342 and the sacrificial insulating cap layer370. Each vertical semiconductor channel (60A, 60B) within the firstmemory stack structures 55A comprises a tubular section that underlie ahorizontal plane including a bottom surface of a drain-select-levelisolation structure 320 and a semi-tubular section overlying the tubularsection and contacting the drain-select-level isolation structure 320.

Referring to FIGS. 30A and 30B, a sacrificial planarization stopperlayer 373 can be formed over the sacrificial insulating cap layer 370.The sacrificial planarization stopper layer 373 includes a material thatcan be used as a planarization stopper structure and is different fromthe material of the sacrificial material layers 42. In one embodiment,the sacrificial planarization stopper layer 373 can include siliconoxide, and can have a thickness in a range from 50 nm to 500 nm.

A photoresist layer (not shown) can be applied over the sacrificialplanarization stopper layer 373, and lithographically patterned to formopenings in areas between clusters of memory stack structures (55A,55B). The pattern in the photoresist layer can be transferred throughthe sacrificial planarization stopper layer 373, the sacrificialinsulating cap layer 370, the drain-select-level sacrificial materiallayer 342, the alternating stack (32, 42), and/or the retro-steppeddielectric material portion 65 using an anisotropic etch to formbackside trenches 79. The backside trenches 79 can extend into thein-process source-level material layers 310′. For example, bottomsurfaces of the backside trenches 79 can be recessed surfaces of thesource-level sacrificial layer 104.

Referring to FIG. 31A, a backside trench spacer 174 may be formed onsidewalls of each backside trench 79. For example, a conformal spacermaterial layer may be deposited in the backside trenches 79 and over thesacrificial planarization stopper layer 373, and may be anisotropicallyetched to form the backside trench spacers 174. The backside trenchspacers 174 include a material that is different from the material ofthe source-level sacrificial layer 104. For example, the backside trenchspacers 174 may include silicon nitride. A backside cavity 79′ ispresent within each backside trench 79.

Referring to FIG. 31B, an etchant that etches the material of thesource-level sacrificial layer 104 selective to the materials of thebackside trench spacers 174, the sacrificial planarization stopper layer373, the upper sacrificial liner 105, and the lower sacrificial liner103 may be introduced into the backside cavities 79′ in an isotropicetch process. For example, if the source-level sacrificial layer 104includes undoped amorphous silicon or an undoped amorphoussilicon-germanium alloy, the backside trench spacers 174 include siliconnitride, and the upper and lower sacrificial liners (105, 103) includesilicon oxide, a wet etch process using hot trimethyl-2 hydroxyethylammonium hydroxide (“hot TMY”) or tetramethyl ammonium hydroxide (TMAH)may be used to remove the source-level sacrificial layer 104 selectiveto the backside trench spacers 174 and the upper and lower sacrificialliners (105, 103). A source cavity 109 is formed in the volume fromwhich the source-level sacrificial layer 104 is removed.

Wet etch chemicals such as hot TMY and TMAH are selective to dopedsemiconductor materials such as the p-doped semiconductor materialand/or the n-doped semiconductor material of the upper source-levelsemiconductor layer 116 and the lower source-level semiconductor layer112. Thus, use of selective wet etch chemicals such as hot TMY and TMAHfor the wet etch process that forms the source cavity 109 provides alarge process window against etch depth variation during formation ofthe backside trenches 79. Specifically, even if sidewalls of the uppersource-level semiconductor layer 116 are physically exposed or even if asurface of the lower source-level semiconductor layer 112 is physicallyexposed upon formation of the source cavity 109 and/or the backsidetrench spacers 174, collateral etching of the upper source-levelsemiconductor layer 116 and/or the lower source-level semiconductorlayer 112 is minimal, and the structural change to the exemplarystructure caused by accidental physical exposure of the surfaces of theupper source-level semiconductor layer 116 and/or the lower source-levelsemiconductor layer 112 during manufacturing steps do not result indevice failures. Each of the memory opening fill structures 58 isphysically exposed to the source cavity 109. Specifically, each of thememory opening fill structures 58 includes a sidewall and a bottomsurface that are physically exposed to the source cavity 109.

Referring to FIG. 31C, a sequence of isotropic etchants, such as wetetchants, may be applied to the physically exposed portions of thememory films 50 to sequentially etch the various component layers of thememory films 50 from outside to inside, and to physically exposecylindrical surfaces of the vertical semiconductor channels 60 at thelevel of the source cavity 109. The upper and lower sacrificial liners(105, 103) may be collaterally etched during removal of the portions ofthe memory films 50 located at the level of the source cavity 109. Thesource cavity 109 may be expanded in volume by removal of the portionsof the memory films 50 at the level of the source cavity 109 and theupper and lower sacrificial liners (105, 103). A top surface of thelower source-level semiconductor layer 112 and a bottom surface of theupper source-level semiconductor layer 116 may be physically exposed tothe source cavity 109. The source cavity 109 is formed by isotropicallyetching the source-level sacrificial layer 104 and a bottom portion ofeach of the memory films 50 selective to at least one source-levelsemiconductor layer (such as the lower source-level semiconductor layer112 and the upper source-level semiconductor layer 116) and the verticalsemiconductor channels 60.

Referring to FIG. 31D, a semiconductor material having a doping of thesecond conductivity type may be deposited on the physically exposedsemiconductor surfaces around the source cavity 109. The physicallyexposed semiconductor surfaces include bottom portions of outersidewalls of the vertical semiconductor channels 60 and a dopedhorizontal surface of the at least one source-level semiconductor layer(such as a bottom surface of the upper source-level semiconductor layer116 and/or a top surface of the lower source-level semiconductor layer112). For example, the physically exposed semiconductor surfaces mayinclude the bottom portions of outer sidewalls of the verticalsemiconductor channels 60, the top horizontal surface of the lowersource-level semiconductor layer 112, and the bottom surface of theupper source-level semiconductor layer 116.

In one embodiment, the doped semiconductor material having a doping ofthe second conductivity type may be deposited on the physically exposedsemiconductor surfaces around the source cavity 109 by a selectivesemiconductor deposition process. A semiconductor precursor gas, anetchant, and a dopant gas may be flowed concurrently into a processchamber including the exemplary structure during the selectivesemiconductor deposition process. For example, the semiconductorprecursor gas may include silane, disilane, or dichlorosilane, theetchant gas may include gaseous hydrogen chloride, and the dopant gasmay include a hydride of a dopant such as phosphine, arsine, stibine, ordiborane. In this case, the selective semiconductor deposition processgrows a doped semiconductor material from physically exposedsemiconductor surfaces around the source cavity 109. The deposited dopedsemiconductor material forms a source contact layer 114, which maycontact sidewalls of the vertical semiconductor channels 60. The atomicconcentration of the dopants of the second conductivity type in thedeposited semiconductor material may be in a range from 1.0×10²⁰/cm³ to2.0×10²¹/cm³, such as from 2.0×10²⁰/cm³ to 8.0×10²⁰/cm³. The sourcecontact layer 114 as initially formed may consist essentially ofsemiconductor atoms and dopant atoms of the second conductivity type.Alternatively, at least one non-selective doped semiconductor materialdeposition process may be used to form the source contact layer 114.Optionally, one or more etch back processes may be used in combinationwith a plurality of selective or non-selective deposition processes toprovide a seamless and/or voidless source contact layer 114.

The duration of the selective semiconductor deposition process may beselected such that the source cavity 109 is filled with the sourcecontact layer 114, and the source contact layer 114 contacts bottom endportions of inner sidewalls of the backside trench spacers 174. In oneembodiment, the source contact layer 114 may be formed by selectivelydepositing a doped semiconductor material from semiconductor surfacesaround the source cavity 109. In one embodiment, the doped semiconductormaterial may include doped polysilicon. Thus, the source-levelsacrificial layer 104 may be replaced with the source contact layer 114.

The layer stack including the lower source-level semiconductor layer112, the source contact layer 114, and the upper source-levelsemiconductor layer 116 constitutes a buried source layer (112, 114,116). The set of layers including the buried source layer (112, 114,116), the source-level insulating layer 117, and the source-select-levelconductive layer 118 constitutes source-level material layers 310, whichreplaces the in-process source-level material layers 310′.

Referring to FIG. 31E, the backside trench spacers 174 may be removedselective to the insulating layers 32, the sacrificial planarizationstopper layer 373, the drain-select-level isolation structures 320, andthe source contact layer 114 using an isotropic etch process. Forexample, if the backside trench spacers 174 include silicon nitride, awet etch process using hot phosphoric acid may be performed to removethe backside trench spacers 174. In one embodiment, the isotropic etchprocess that removes the backside trench spacers 174 may be combinedwith a subsequent isotropic etch process that etches the sacrificialmaterial layers 42 selective to the insulating layers 32,drain-select-level isolation structures 320, the sacrificialplanarization stopper layer 373, and the source contact layer 114.

The vertical semiconductor channels 60 have a doping of the firstconductivity type, and the source contact layer 114 having a doping ofthe second conductivity type that is an opposite of the firstconductivity type is located over the substrate that includes thesubstrate semiconductor layer 9. The source contact layer 114 contactsbottom ends of each of the vertical semiconductor channels 60.

An oxidation process may be performed to convert physically exposedsurface portions of semiconductor materials into dielectricsemiconductor oxide portions. For example, surfaces portions of thesource contact layer 114 and the upper source-level semiconductor layer116 may be converted into dielectric semiconductor oxide plates 122, andsurface portions of the source-select-level conductive layer 118 may beconverted into annular dielectric semiconductor oxide spacers 124.

Referring to FIG. 32, the sacrificial material layers 42 may be removedselective to the insulating layers 32, the drain-select-level isolationstructures 320, the sacrificial planarization stopper layer 373, and thesource contact layer 114, the dielectric semiconductor oxide plates 122,and the annular dielectric semiconductor oxide spacers 124. For example,an etchant that selectively etches the materials of the sacrificialmaterial layers 42 with respect to the materials of the insulatinglayers 32, the drain-select-level isolation structures 320, theretro-stepped dielectric material portion 65, and the material of theoutermost layer of the memory films (50A, 50B) may be introduced intothe backside trenches 79, for example, using an isotropic etch process.For example, the sacrificial material layers 42 may include siliconnitride, the materials of the insulating layers 32, thedrain-select-level isolation structures 320, the retro-steppeddielectric material portion 65, and the outermost layer of the memoryfilms (50A, 50B) may include silicon oxide materials.

The isotropic etch process may be a wet etch process using a wet etchsolution, or may be a gas phase (dry) etch process in which the etchantis introduced in a vapor phase into the backside trench 79. For example,if the sacrificial material layers 42 include silicon nitride, the etchprocess may be a wet etch process in which the exemplary structure isimmersed within a wet etch tank including phosphoric acid, which etchessilicon nitride selective to silicon oxide, silicon, and various othermaterials used in the art.

Backside recesses 43 are formed in volumes from which the sacrificialmaterial layers 42 are removed. Each of the backside recesses 43 may bea laterally extending cavity having a lateral dimension that is greaterthan the vertical extent of the cavity. In other words, the lateraldimension of each of the backside recesses 43 may be greater than theheight of the respective backside recess 43. A plurality of backsiderecesses 43 may be formed in the volumes from which the material of thesacrificial material layers 42 is removed. Each of the backside recesses43 may extend substantially parallel to the top surface of the substratesemiconductor layer 9. A backside recess 43 may be vertically bounded bya top surface of an underlying insulating layer 32 and a bottom surfaceof an overlying insulating layer 32. In one embodiment, each of thebackside recesses 43 may have a uniform height throughout. Thedrain-select-level sacrificial material layer 342 is protected from theetchant by a combination of the sacrificial planarization stopper layer373, the drain-select-level isolation structures 320, and a topmostinsulating layer 32, i.e., the topmost one of the insulating layers 32.

Referring to FIG. 33, a backside blocking dielectric layer (not shown)may be optionally deposited in the backside recesses 43 and the backsidetrenches 79 and over the sacrificial planarization stopper layer 373.The backside blocking dielectric layer includes a dielectric materialsuch as a dielectric metal oxide, silicon oxide, or a combinationthereof. For example, the backside blocking dielectric layer may includealuminum oxide. The backside blocking dielectric layer may be formed bya conformal deposition process such as atomic layer deposition orchemical vapor deposition. The thickness of the backside blockingdielectric layer may be in a range from 1 nm to 20 nm, such as from 2 nmto 10 nm, although lesser and greater thicknesses may also be used.

At least one conductive material may be deposited in the plurality ofbackside recesses 43, on the sidewalls of the backside trenches 79, andover the sacrificial planarization stopper layer 373. The at least oneconductive material may be deposited by a conformal deposition method,which may be, for example, chemical vapor deposition (CVD), atomic layerdeposition (ALD), electroless plating, electroplating, or a combinationthereof. The at least one conductive material may include an elementalmetal, an intermetallic alloy of at least two elemental metals, aconductive nitride of at least one elemental metal, a conductive metaloxide, a conductive doped semiconductor material, a conductivemetal-semiconductor alloy such as a metal silicide, alloys thereof, andcombinations or stacks thereof.

In one embodiment, the at least one conductive material may include atleast one metallic material, i.e., an electrically conductive materialthat includes at least one metallic element. Non-limiting exemplarymetallic materials that may be deposited in the backside recesses 43include tungsten, tungsten nitride, titanium, titanium nitride,tantalum, tantalum nitride, cobalt, and ruthenium. For example, the atleast one conductive material may include a conductive metallic nitrideliner that includes a conductive metallic nitride material such as TiN,TaN, WN, or a combination thereof, and a conductive fill material suchas W, Co, Ru, Mo, Cu, or combinations thereof. In one embodiment, the atleast one conductive material for filling the backside recesses 43 maybe a combination of titanium nitride layer and a tungsten fill material.

Electrically conductive layers 46 may be formed in the backside recesses43 by deposition of the at least one conductive material. A continuousmetallic material layer (not shown) may be formed on the sidewalls ofeach backside trench 79 and over the sacrificial planarization stopperlayer 373. Each of the electrically conductive layers 46 may include arespective conductive metallic nitride liner and a respective conductivefill material. Thus, the first and second sacrificial material layers 42may be replaced with the electrically conductive layers 46,respectively. Specifically, each sacrificial material layer 42 may bereplaced with an optional portion of the backside blocking dielectriclayer and an electrically conductive layer 46. A backside cavity ispresent in the portion of each backside trench 79 that is not filledwith the continuous metallic material layer.

Residual conductive material may be removed from inside the backsidetrenches 79. Specifically, the deposited metallic material of thecontinuous metallic material layer may be etched back from the sidewallsof each backside trench 79 and from above the sacrificial planarizationstopper layer 373, for example, by an anisotropic or isotropic etch.Each remaining portion of the deposited metallic material in thebackside recesses 43 constitutes an electrically conductive layer 46.Sidewalls of the electrically conductive layers 46 may be physicallyexposed to a respective backside trench 79. The backside trenches mayhave a pair of curved sidewalls having a non-periodic width variationalong the first horizontal direction hd1 and a non-linear widthvariation along the vertical direction.

Each electrically conductive layer 46 may be a conductive sheetincluding openings therein. A first subset of the openings through eachelectrically conductive layer 46 may be filled with memory opening fillstructures 58. A second subset of the openings through each electricallyconductive layer 46 may be filled with the support pillar structures 20.Each electrically conductive layer 46 may have a lesser area than anyunderlying electrically conductive layer 46 because of the first andsecond stepped surfaces. Each electrically conductive layer 46 may havea greater area than any overlying electrically conductive layer 46because of the first and second stepped surfaces.

The electrically conductive layer 46 can function as combinations of acontrol gate and a word line located at the same level. The control gateelectrodes within each electrically conductive layer 46 are the controlgate electrodes for a vertical memory device including the memory stackstructure (55A, 55B). Each of the memory stack structures (55A, 55B)comprises a vertical stack of memory elements located at each level ofthe electrically conductive layers 46. A subset of the electricallyconductive layers 46 may comprise word lines for the memory elements.The semiconductor devices in the peripheral device region 200 maycomprise word line switch devices configured to control a bias voltageto respective word lines. The memory-level assembly is located over thesubstrate semiconductor layer 9. The memory-level assembly includes atleast one alternating stack (32, 46) and memory stack structures (55A,55B) vertically extending through the at least one alternating stack(32, 46).

Referring to FIG. 34, a dielectric material can be conformally depositedin the backside trenches 79 and over the sacrificial planarizationstopper layer 373 by a conformal deposition process. The dielectricmaterial layer may include, for example, silicon oxide. Each portion ofthe dielectric material deposited in a backside trench 79 constitutes adielectric wall structure 376. The horizontally-extending portion of thedeposited dielectric material above the sacrificial planarizationstopper layer 373 can be removed, for example, by a recess etch, whichcan use, for example, a wet etch or a dry etch. Alternatively, aninsulating spacer (not shown) can be formed at a periphery of eachbackside trench 79, and a backside contact via structure (not shown)contacting the source contact layer 114 can be formed through eachdielectric semiconductor oxide plate 122 within a respective one of theinsulating spacers.

Referring to FIGS. 35A and 35B, the sacrificial planarization stopperlayer 373 and an upper portion of each dielectric wall structures 376can be removed by a recess etch, which can use an isotropic etch processsuch as a wet etch process using hydrofluoric acid. The sacrificialinsulating cap layer 370, an upper portion of each drain-select-levelisolation structure 320, an upper portion of the retro-steppeddielectric material portion 65, and an additional portion of eachdielectric wall structure 376 can be subsequently removed, for example,by extending the recess etch process. In one embodiment, sacrificialplanarization stopper layer 373, the sacrificial insulating cap layer370, the drain-select-level isolation structures 320, the retro-steppeddielectric material portion 65, and the dielectric wall structures 376can include a same dielectric material, which may be, for example,undoped silicate glass or doped silicate glass. In this case, the recessetch process can provide recessed surfaces of the drain-select-levelisolation structures 320, the retro-stepped dielectric material portion65, and the dielectric wall structures 376 within a same horizontalplane. A top surface of each strip of the drain-select-level sacrificialmaterial layer 342 can be physically exposed after recessing thesacrificial planarization stopper layer 373, the sacrificial insulatingcap layer 370, the drain-select-level isolation structures 320, theretro-stepped dielectric material portion 65, and the dielectric wallstructures 376.

The recess etch process used to recess the sacrificial planarizationstopper layer 373, the sacrificial insulating cap layer 370, thedrain-select-level isolation structures 320, the retro-steppeddielectric material portion 65, and the dielectric wall structures 376can be selective to the materials of the drain-select-level sacrificialmaterial layer 342, the drain regions (63A, 63B), the verticalsemiconductor channels (60A, 60B), and a material layer within thememory films (50A, 50B) such as a charge storage layer 54. For example,the recess etch process can include a wet etch process using dilutehydrofluoric acid.

Referring to FIG. 36, drain-select-level recesses 343 are formed byremoving the drain-select-level sacrificial material layer 342 selectiveto the materials of the drain-select-level isolation structures 320, theretro-stepped dielectric material portion 65, and the dielectric wallstructures 376, selective to the semiconductor materials of the drainregions (63A, 63B) and the vertical semiconductor channels (60A, 60B),and selective to the dielectric material of the outermost layer of thememory films (50A, 50B) (which may be, for example, silicon oxide of theblocking dielectric layers 52). For example, a wet etch process usinghot phosphoric acid may be used to remove the drain-select-levelsacrificial material layer 342. The volumes from which thedrain-select-level sacrificial material layer 342 is removed constitutesthe drain-select-level recesses 343.

Referring to FIGS. 37A and 37B, at least one conductive material can bedeposited in the drain-select-level recesses 343 and over thedrain-select-level isolation structures 320, the retro-steppeddielectric material portion 65, and the dielectric wall structures 376.Portions of the at least one deposited conductive material that overliethe drain-select-level isolation structures 320, the retro-steppeddielectric material portion 65, and the dielectric wall structures 376are etched back, for example, by a recess etch. Portions of the at leastone conductive material that fill the drain-select-level recesses 343constitute a drain-select-level electrically conductive layer 346. Thedrain-select-level electrically conductive layer 346 is an electricallyconductive layer that is formed at the drain select level, i.e., a levelat which drain select level electrodes. The drain-select-levelelectrically conductive layer 346 are formed as multiplephysically-disjoined fingers that are laterally electrically isolatedone from another by the drain-select-level isolation structures 320.

Each strip of the drain-select-level electrically conductive layer 346laterally extends along the first horizontal direction hd1. Each stripof the drain-select-level electrically conductive layer 346 can have twopairs of laterally undulating sidewalls that extend along the firsthorizontal direction hd1. Each laterally undulating sidewall of a stripof the drain-select-level electrically conductive layer 346 can have alaterally alternating sequence of planar sidewall segments and concavesidewall segments. Each strip of the drain-select-level electricallyconductive layer 346 contacts two rows of first memory stack structures55A. In case second memory stack structures 55B are present, a strip ofthe drain-select-level electrically conductive layer 346 can contact oneor more rows of second memory stack structures 55B.

In one embodiment, each strip of the drain-select-level electricallyconductive layer 346 can include a combination of a drain-select-levelmetallic liner 346A and a drain-select-level metal fill portion 346B.The drain-select-level metallic liner 346A includes an electricallyconductive metallic material that can function as a diffusion barrierlayer and/or adhesion promotion layer for a metallic fill material to besubsequently deposited. The drain-select-level metallic liner 346A caninclude a conductive metallic nitride material such as TiN, TaN, WN, ora stack thereof, or can include a conductive metallic carbide materialsuch as TiC, TaC, WC, or a stack thereof. The drain-select-levelmetallic liner 346A can be deposited by a conformal deposition processsuch as chemical vapor deposition (CVD) or atomic layer deposition(ALD), or by a non-conformal deposition process such as physical vapordeposition (PVD). The thickness of the drain-select-level metallic liner346A can be in a range from 2 nm to 8 nm, such as from 3 nm to 6 nm,although lesser and greater thicknesses can also be used. In oneembodiment, the drain-select-level metallic liner 346A can consistessentially of a conductive metal nitride such as TiN.

The drain-select-level metal fill portion 346B can be deposited by aconformal or non-conformal deposition method, which can be, for example,chemical vapor deposition (CVD), atomic layer deposition (ALD), physicalvapor deposition (PVD), electroless plating, electroplating, or acombination thereof. In one embodiment, the drain-select-level metalfill portion 346B can consist essentially of at least one elementalmetal. The at least one elemental metal of the drain-select-level metalfill portion 346B can be selected, for example, from tungsten, cobalt,ruthenium, titanium, and tantalum. In one embodiment, thedrain-select-level metal fill portion 346B can consist essentially of asingle elemental metal.

The drain-select-level electrically conductive layer 346 is formed on atopmost one of the insulating layers 32, and is added to the alternatingstack (32, 46) as a topmost electrically conductive layer. Eachdrain-select-level isolation structure 320 that does not contact abackside trench 79 vertically extends through the drain-select-levelelectrically conductive layer 346, which is a topmost electricallyconductive layer within an expanded alternating stack (32, 46, 346).Each strip of the drain-select-level electrically conductive layer 346includes a drain-select-level metallic liner 346A and adrain-select-level metal fill portion 346B embedded within thedrain-select-level metallic liner 346A.

Referring to FIGS. 38A and 38B, a contact level dielectric layer 73 canbe formed over the drain-select-level electrically conductive layer 346by deposition and planarization of a dielectric material such as siliconoxide. The contact level dielectric layer 73 contacts top surfaces ofthe drain-select-level metallic liner 346A and the drain-select-levelmetal fill portion 346B of each strip of the drain-select-levelelectrically conductive layer 346, i.e., the topmost electricallyconductive layer of the expanded alternating stack (32, 46, 346).

Additional contact via structures (88, 86) can be formed through thecontact level dielectric layer 73, and optionally through theretro-stepped dielectric material portion 65. For example, drain contactvia structures 88 can be formed through the contact level dielectriclayer 73 on each drain region (63A, 63B). Word line contact viastructures 86 can be formed on the electrically conductive layers 46through the contact level dielectric layer 73, and through theretro-stepped dielectric material portion 65. Peripheral device contactvia structures (not shown) can be formed through the retro-steppeddielectric material portion 65 directly on respective nodes of theperipheral devices.

Referring to all drawings of the first, second, and third exemplarystructures and according to various embodiments of the presentdisclosure, a three-dimensional memory device is provided, whichcomprises: an alternating stack of insulating layers 32 and electricallyconductive layers (46 and 346 if present) located over a substrate (9and 10 if present); first memory stack structures 55A extending throughthe alternating stack (32, 46, 346), wherein each of the first memorystack structures 55A includes a respective first memory film (50, 50A)and a respective first vertical semiconductor channel (60, 60A); and adrain-select-level isolation structure 320 having a pair of straightlengthwise sidewalls that extend along a first horizontal direction hd1and contact straight sidewalls of the first memory stack structures 55A,wherein each first vertical semiconductor channel (60, 60A) comprises atubular section that underlie a horizontal plane including a bottomsurface of the drain-select-level isolation structure 320 and asemi-tubular section overlying the tubular section and contacting thedrain-select-level isolation structure 320.

In one embodiment, each of the first vertical semiconductor channels(60, 60A) comprises: a tubular vertical semiconductor channel segmentthat extends through a first plurality of electrically conductive layers46 of the alternating stack (32, 46, 346) that are located under thehorizontal plane; and a semi-tubular vertical semiconductor channelsegment that overlies the tubular vertical semiconductor channel segmentand contacts a respective one of the pair of straight lengthwisesidewalls of the drain-select-level isolation structure 320.

In one embodiment, the three-dimensional memory device comprises firstdielectric cores 62A located within a respective one of the first memorystack structures 55A, wherein each of the first dielectric cores 62Acomprises: a cylindrical core portion that extends through the firstplurality of electrically conductive layers 46 of the alternating stack(32, 46, 346) that are located under the horizontal plane; and asemi-cylindrical portion that overlies the tubular verticalsemiconductor channel segment and contacts a respective one of the pairof straight lengthwise sidewalls of the drain-select-level isolationstructure 320.

In one embodiment, the first vertical semiconductor channels (60, 60A)have a doping of a first conductivity type; and first drain regions 63Ahaving a doping of a second conductivity type are located at an upperend of each of the first vertical semiconductor channels (60, 60A).

In one embodiment, each of the first drain regions 63A has a straightsidewall that contacts a respective one of the pair of straightlengthwise sidewalls of the drain-select-level isolation structure 320.

In one embodiment, the drain-select-level isolation structure 320vertically extends through a plurality of electrically conductive layers(46 or 346) including a topmost one of the electrically conductivelayers within the alternating stack (32, 46, 346).

In one embodiment, the drain-select-level isolation structure 320vertically extends through a topmost one of the electrically conductivelayers 346 within the alternating stack (32, 46, 346); the topmost oneof the electrically conductive layers 346 comprises a drain-select-levelmetallic liner 346A and a drain-select-level metal fill portion 346Bembedded within the drain-select-level metallic liner 346A; and adielectric layer (such as a contact level dielectric layer 73) contactstop surfaces of the drain-select-level metallic liner 346A and thedrain-select-level metal fill portion 346B.

In one embodiment, the substrate (9, 10) comprises a semiconductormaterial layer 10; the semiconductor material layer 10 and the firstvertical semiconductor channels 60 have a doping of a first conductivitytype; pedestal channel portions 11 are disposed between bottom ends ofthe first vertical semiconductor channels 60 and the semiconductormaterial layer 10; and a source region 61 having a doping of a secondconductivity type is embedded within the semiconductor material layer 10and is laterally spaced from the first memory stack structures 55A andthe pedestal channel portions 11.

In one embodiment, the first vertical semiconductor channels 60A have adoping of a first conductivity type; a source contact layer 114 having adoping of a second conductivity type that is an opposite of the firstconductivity type is located over the substrate 9; and the sourcecontact layer 114 contacts bottom ends of each of the first verticalsemiconductor channels 60A.

In one embodiment, the three-dimensional memory device comprises secondmemory stack structures 55B extending through the alternating stack (32,46, 346). Each of the second memory stack structures 55B includes arespective second memory film (50, 50B) and a respective second verticalsemiconductor channel (60, 60B); and each second vertical semiconductorchannel (60, 60B) has a tubular configuration and extends through eachelectrically conductive layer (46, 346) in the alternating stack (32,46, 346).

In one embodiment, the first memory stack structures 55A are arranged infirst rows that extend along a first horizontal direction hd1 and have auniform intra-row pitch p1 within each first row. The second memorystack structures 55B are arranged in second rows that extend along thefirst horizontal direction hd1 and have the uniform intra-row pitch p1within each second row. The first memory stack structures 55A and thesecond memory stack structures 55B are arranged as a two-dimensionalperiodic array in which each neighboring pair of rows among the firstrows and second rows has a uniform inter-row pitch p2.

In one embodiment, the three-dimensional memory device further comprisesa pair of backside trenches 79 vertically extending through thealternating stack (32, 46, 346) and laterally extending along the firsthorizontal direction hd1, wherein the two-dimensional periodic array andthe drain-select-level isolation structure 320 are located between thepair of backside trenches 79.

In one embodiment, the three-dimensional memory device comprises: firstdrain regions 63A contacting an upper end of a respective one of thefirst vertical semiconductor channels (60, 60A) and having asemi-cylindrical shape; second drain regions 63B contacting an upper endof a respective one of the second vertical semiconductor channels (60,60B) and having a cylindrical shape; first drain contact via structures88 having bottommost surfaces that contact topmost surfaces of the firstdrain regions 63A; and second drain contact via structures 88 contactinga top surface and a sidewall of a respective one of the second drainregions 63B.

Referring to FIGS. 39A and 39B, a fourth exemplary structure accordingto a fourth embodiment of the present disclosure can be derived from thesecond exemplary structure of FIG. 18. Generally, the fourth exemplarystructure can be provided by forming an alternating stack of insulatinglayers 32 and spacer material layers over a substrate (9 and optionally10). The spacer material layers are formed as electrically conductivelayers 46, or are formed as sacrificial material layers 42 and aresubsequently replaced with the electrically conductive layers 46. Memorystack structures 55 extending through the alternating stack (32, 46) areformed. Each of the memory stack structures 55 includes a respectivememory film 50 and a respective vertical semiconductor channel 60including dopants of a first conductivity type at a first atomicconcentration. Drain regions 63 having a doping of a second conductivitytype that is an opposite of the first conductivity type is formed on anupper end of each of the vertical semiconductor channels 60. The memorystack structures 55 can be arranged in two rows that extend along afirst horizontal direction hd1. The memory stack structures 55 arearranged as a two-dimensional periodic array in which each neighboringpair of rows of memory stack structures 55 has a uniform inter-row pitchp2. Each two-dimensional periodic array of memory stack structures 55can be formed between the pair of backside trenches 79.

A patterned etch mask layer 327 including elongated openings can beformed over the alternating stack (32, 46) and the memory stackstructures 55. In one embodiment, the patterned etch mask layer 327 canbe a patterned photoresist layer formed by application and lithographicpatterning of a photoresist material over the alternating stack (32, 46)and the memory stack structures 55. Each opening in the patterned etchmask layer 327 can overlie a segment of each memory stack structure 55within a neighboring pair of rows of memory stack structures 55. Eachmemory stack structure 55 of which a segment is located within an areaof one of the openings in the patterned etch mask layer 327 is hereinreferred to as a first memory stack structure 55A. Each memory openingfill structure 58 including a first memory stack structure 55A is hereinreferred to as a first memory opening fill structure 58A. Memory stackstructures 55 that are entirely covered with the patterned etch masklayer 327, for example, by being located between neighboring pairs offirst memory stack structures 55A, are herein referred to as a secondmemory stack structure 55B. Second memory stack structures 55B may, ormay not, be present in the first exemplary structure depending on thelayout of the elongated openings in the patterned etch mask layer 327.Each memory opening fill structure 58 including a second memory stackstructure 55B is herein referred to as a second memory opening fillstructure 58B.

Each first memory stack structure 55A is only partly covered with thepatterned etch mask layer 327. As such, a first area of each of thefirst memory stack structures 55A is located within an area of anelongated opening in the patterned etch mask layer 327, and a secondarea of each of the first memory stack structures 55A is covered by thepatterned etch mask layer 327. The first area can be in a range from 15%to 70%, such as from 25% to 50%, of the entire area of each first memorystack structure 55A.

An anisotropic etch process is performed to etch unmasked portions ofthe insulating cap layer 70 and upper layers of the alternating stack(32, 46) located at the drain select levels without etching the memorystack structures 55. A drain-select-level trench 309 is formedunderneath each elongated opening within the patterned etch mask layer327 by etching through an upper portion of the alternating stack (32,46) selective to the physically exposed material portions of the memoryopening fill structures 58. Each drain-select-level trench 309 caninclude a pair of laterally undulating lengthwise sidewalls that extendgenerally along the first horizontal direction hd1. Each laterallyundulating lengthwise sidewall can include a laterally alternatingsequence of straight sidewall segments (that are sidewalls of theinsulating cap layer 70 and upper layers of the alternating stack (32,46)) and concave sidewall segments (that are sidewalls of the memoryopening fill structures 58). The depth of the drain-select-leveltrenches 309 can be selected such that the drain-select-level trenches309 vertically extend through each electrically conductive layer 46located at drain select levels, i.e., levels in which the electricallyconductive layers function as drain select level gate electrodes. Eachvertical semiconductor channel 60 of the memory stack structures 55 hasa tubular configuration.

The anisotropic etch process partially physically exposes upper portionsof sidewalls of two rows of the first memory stack structures 55A aroundeach drain-select-level trench 309. Each drain-select-level trench 309extends through an upper portion of the alternating stack (32, 46) andlaterally extends between two rows of first memory stack structures 55A.The memory stack structures 55 includes first memory stack structures55A that are partially exposed to a respective one of thedrain-select-level trenches 309, and optionally includes second memorystack structures 55B that are masked with the patterned etch mask layer317 during formation of the drain-select-level trenches 309. Thus,sidewalls of the second memory stack structures 55B are not physicallyexposed after formation of the drain-select-level trenches 309.

Referring to FIGS. 40A and 40B, dopants of the first conductivity typeare implanted into segments of vertical semiconductor channels 60 withinthe first memory stack structures 55A that are proximal to a respectiveone of the drain-select-level trenches 309. Angled ion implantation canbe performed using the patterned etch mask layer 307 as an implantationmask. The tilt angle of the angled ion implantation process can beselected such that the dopants of the first conductivity type areimplanted into portions of the vertical semiconductor channels 60 thatare located above the horizontal plane including the top surface of atopmost electrically conductive layer 46 that underlies thedrain-select-level trenches 309. For example, the tilt angle of the ionimplantation process can be in a range from 2 degree to 30 degrees, suchas from 4 degrees to 15 degrees, although lesser and greater tilt anglescan also be used. In case the first conductivity type is p-type, thedopants of the first conductivity type can include boron atoms. In casethe first conductivity type is n-type, the dopants of the firstconductivity type can include phosphor atoms, arsenic atoms, and/orantimony atoms. In one embodiment, diffusion suppressor atoms such ascarbon atoms may be implanted in addition to the dopant atoms of thefirst conductivity type to reduce diffusion of the implanted dopants ofthe first conductivity type.

Each vertical semiconductor channel 60 within the first memory stackstructures 55A (located within the first memory opening fill structures58A) comprises a tubular section 60T including dopants of the firstconductivity type at the first atomic concentration (which is the atomicconcentration of dopants of the first conductivity type as providedduring formation of the first and second semiconductor channel layers(601, 602)), a first semi-tubular section 60S overlying the tubularsection 60T and including dopants of the first conductivity type at thefirst atomic concentration, and a second semi-tubular section 60Uoverlying the tubular section 60T and laterally adjoined to the firstsemi-tubular section 60S and including dopants of the first conductivitytype at a second atomic concentration that is greater than the firstatomic concentration.

In one embodiment, the second atomic concentration can be in a rangefrom 5 times the first atomic concentration to 1.0×10⁵ times the firstatomic concentration. In a non-limiting illustrative example, the firstatomic concentration can be in a range from 1.0×10¹⁴/cm³ to1.0×10¹⁸/cm³, and the second atomic concentration can be in a range from1.0×10¹⁷/cm³ to 1.0×10¹⁹/cm³, although lesser and greater concentrationscan be used for each of the first atomic concentration and the secondatomic concentration. In one embodiment, the tubular section 60T of eachfirst memory stack structure 55A (within a respective one of the firstmemory opening fill structures 58A) can be located underneath ahorizontal plane including bottom surfaces of the drain-select-leveltrenches 309. Each tubular section 60T, each first semi-tubular section60S, and each second semi-tubular section 60U can include a respectiveportion derived from a first semiconductor channel layer 601 and arespective portion derived from a second semiconductor channel layer602. The second semi-tubular section 60U may additionally include carbonatoms, for example, at an atomic concentration in a range from1.0×10¹⁵/cm³ to 5.0×10¹⁷/cm³, and the first semi-tubular section 60S andthe tubular section 60T may be free of carbon atoms, e.g., at a tracelevel below 1.0×10¹⁴/cm³. Thus, the atomic concentration of carbon atomsin the second semi-tubular section 60U can be at least 10 times theatomic concentration of carbon atoms in the first semi-tubular region60S, and at least 10 times the atomic concentration of carbon atoms inthe tubular region 60T.

The memory stack structures 55 can include second memory stackstructures 55B extending through the alternating stack (32, 46). Each ofthe second memory stack structures 55B includes a respective secondmemory film 50 and a respective second vertical semiconductor channel60, and each second vertical semiconductor channel 60 can include aportion having a tubular configuration, extend through each electricallyconductive layer 46 in the alternating stack (32, 46), and includedopants of the first conductivity type at the first atomic concentrationthroughout an entire volume thereof. The portion having the tubularconfiguration can extend to the horizontal plane including the topsurfaces of the drain regions 63.

In one embodiment, each of the first semi-tubular sections 60S has ahorizontal cross-sectional shape of a first block arc that is invariantwith translation along a vertical direction hd1, and each of the secondsemi-tubular sections 60U has a horizontal cross-sectional shape of asecond block arc that is invariant with translation along the verticaldirection. As used herein, a “block arc” is a shape that is obtained bylimiting the azimuthal extent of a planar annular shape to less than 360degrees around the geometrical center of the planar annular shape (i.e.,the shape of an anulus within a Euclidean plane).

Dopants of the first conductivity type are collaterally implanted into asegment of each of the first drain regions 63 during implantation of thedopants of the first conductivity type into the implanted segments ofvertical semiconductor channels 60 (i.e., into the second semi-tubularsections 60U). The first drain regions 63 can contact an upper end of arespective one of the first semi-tubular sections 60S, contact an upperend of a respective one of the second semi-tubular sections 60U, andhave a doping of the second conductivity type that is the opposite ofthe first conductivity type. In one embodiment, each of the first drainregions 63 can include a first drain segment 631 consisting essentiallyof a semiconductor material and dopants of the second conductivity typeand contacting the upper end of the respective one of the firstsemi-tubular sections 60S, and a second drain segment 632 consistingessentially of the semiconductor material, dopants of the secondconductivity type, and dopants of the first conductivity type, andcontacting the upper end of the respective one of the secondsemi-tubular sections 60U. The atomic concentration of dopants of thefirst conductivity type in a second drain segment 632 is less than theatomic concentration of dopants of the second conductivity type in thesecond drain segment 632, and can be the less than the atomicconcentration of dopants of the first conductivity type in the secondsemi-tubular sections 60U. The patterned etch mask layer 327 can beremoved, for example, by ashing after formation of thedrain-select-level trenches 309.

Referring to FIGS. 41A and 41B, drain-select-level isolation structure322 can be formed in each drain-select-level trench 309, for example, bydepositing a dielectric material such as silicon oxide in thedrain-select-level trenches 309. Excess portions of the dielectricmaterial can be removed from above the horizontal plane including thetop surface of the insulating cap layer 70 by a planarization process,which can use a recess etch and/or chemical mechanical planarization.Each drain-select-level isolation structure 322 can be formed in adrain-select-level trench 309 on sidewalls of memory films 50 of thefirst memory stack structures 55A. Each drain-select-level isolationstructure 320 can include a pair of laterally-undulating sidewalls thatlaterally extend along the first horizontal direction hd1 and includinga laterally alternating sequence of straight sidewall segments andconcave sidewall segments. Each drain-select-level isolation structure322 can vertically extend through each electrically conductive layer 46within the alternating stack (32, 46) that is located at a drain selectlevel.

In one embodiment, the first memory stack structures 55A are arranged infirst rows that extend along the first horizontal direction hd1 and hasa uniform intra-row pitch p1 within each first row. The second memorystack structures 55B are arranged in second rows that extend along thefirst horizontal direction hd1 and have the uniform intra-row pitch p1within each second row. The first memory stack structures 55A and thesecond memory stack structures 55B are arranged as a two-dimensionalperiodic array in which each neighboring pair of rows among the firstrows and second rows has a uniform inter-row pitch p2.

In one embodiment, a pair of backside trenches 79 vertically extendsthrough the alternating stack (32, 46) and laterally extends along thefirst horizontal direction hd1. The two-dimensional periodic array ofmemory stack structures 55 and at least one drain-select-level isolationstructure 322 are located between the pair of backside trenches 79.

Referring to FIG. 42, a contact level dielectric layer 73 can be formedover the insulating cap layer 70, the drain-select-level isolationstructures 322, and over the memory stack structures 55 and the supportpillar structures 20. The contact level dielectric layer 73 includes adielectric material such as silicon oxide. The contact level dielectriclayer 73 can have a thickness in a range from 50 nm to 500 nm, althoughlesser and greater thicknesses can also be used.

Referring to FIGS. 43A-43C, additional contact via structures (88, 86)can be formed through the contact level dielectric layer 73, andoptionally through the retro-stepped dielectric material portion 65. Forexample, drain contact via structures 88 can be formed through thecontact level dielectric layer 73 on each drain region 63. Word linecontact via structures 86 can be formed on the electrically conductivelayers 46 through the contact level dielectric layer 73, and through theretro-stepped dielectric material portion 65. Peripheral device contactvia structures (not shown) can be formed through the retro-steppeddielectric material portion 65 directly on respective nodes of theperipheral devices.

The drain-select-level gate electrodes, embodied as a subset of theelectrically conductive layers 46, are self-aligned to the memoryopening fill structures. Separation of the drain-select-level gateelectrodes is performed after replacement of the sacrificial materiallayers 42 with the electrically conductive layers 46. Separateprocessing steps for replacement of sacrificial material layers 42 atthe drain select levels is not necessary, and thus, total processingcost can be reduced. The drain-select-level gate electrodes arelaterally spaced among one another by drain-select-level isolationstructure 320 and second semi-tubular sections 60U that are inactiveportions of a vertical semiconductor channel.

In one embodiment, the insulating layers 32 can include silicon oxideand the electrically conductive layers 46 can include tungsten. In thiscase, formation of the drain-select-level trenches 309 can be performedby employing an anisotropic etch process that etches silicon oxide andtungsten selective to the materials of the memory opening fillstructures 58. Thus, the drain-select-level trenches 309 can beself-aligned to the memory opening fill structures 58. A bottom surfaceof each drain-select-level trenches 309 can be formed on an insulatinglayer 32 located between a topmost word line and a bottommostdrain-select-level gate electrode. The implantation of the dopants ofthe first conductivity type (such as boron in case the firstconductivity type is p-type) into the second semi-tubular sections 60Uof the vertical semiconductor channels 60 raises the threshold voltageof the second semi-tubular sections 60U, effectively disabling thesecond semi-tubular sections 60U and preventing flow of electricalcurrent therethrough. In other words, high bias voltages applied toadjacent drain-select-level gate electrodes do not turn on the secondsemi-tubular sections 60U of the vertical semiconductor channels 60, anda leakage current through the second semi-tubular sections 60U isprevented by the high dose of the dopants of the first conductivity typeduring the angled implantation process.

Formation of the drain-select-level trenches 309 enables implantation ofthe first conductivity dopants into the second semi-tubular sections60U. The angled implantation can be a low energy implantation process,which reduces straggle of implanted dopants and reduces electricalimpact on the first semi-tubular sections 60S of the verticalsemiconductor channels 60, i.e., does not affect the threshold voltageof the first semi-tubular sections 60S. High temperature thermal annealprocesses can be performed prior to implantation of the dopants of thefirst conductivity type into the second semi-tubular sections 60U. Thus,outdiffusion of the first conductivity type dopants from the secondsemi-tubular sections 60U after the angled ion implantation process canbe limited due to reduced thermal cycling. Thus, the impact of formationof the second semi-tubular sections 60U on the threshold voltage of thefirst semi-tubular sections 60S can be minimal.

High threshold voltage for the second semi-tubular sections 60U can beeffectively provided by a multi-twist ion implantation process tominimize shadowing of the implanted dopants due to geometry. The dose,the tilt angle, and the energy of the ion implantation process thatimplants the dopants of the first conductivity type into the secondsemi-tubular sections 60U can be optimized based on the diffusivity ofthe dopants of the first conductivity type and the subsequent thermalbudget. In some embodiments, portions of the memory films 50 may be atleast partially removed prior to the ion implantation process, in whichcase the parameters of the ion implantation process may be adjustedaccordingly.

Referring to FIGS. 44A and 44B, a fifth exemplary structure according toa fifth embodiment of the present disclosure can be derived from thefirst exemplary structure of FIG. 6. Generally, the fifth exemplarystructure can be provided by forming an alternating stack of insulatinglayers 32 and spacer material layers over a substrate (9 and optionally10). The spacer material layers are formed as sacrificial materiallayers 42, and can be subsequently replaced with the electricallyconductive layers. Memory stack structures 55 extending through thealternating stack (32, 42) are formed. Each of the memory stackstructures 55 includes a respective memory film 50 and a respectivevertical semiconductor channel 60 including dopants of a firstconductivity type at a first atomic concentration. Drain regions 63having a doping of a second conductivity type that is an opposite of thefirst conductivity type is formed on an upper end of each of thevertical semiconductor channels 60. The memory stack structures 55 canbe arranged in two rows that extend along a first horizontal directionhd1. The memory stack structures 55 are arranged as a two-dimensionalperiodic array in which each neighboring pair of rows of memory stackstructures 55 has a uniform inter-row pitch p2. Each two-dimensionalperiodic array of memory stack structures 55 can be formed between thepair of backside trenches 79.

A patterned etch mask layer 327 including elongated openings can beformed over the alternating stack (32, 42) and the memory stackstructures 55. In one embodiment, the patterned etch mask layer 327 canbe a patterned photoresist layer formed by application and lithographicpatterning of a photoresist material over the alternating stack (32, 42)and the memory stack structures 55. Each opening in the patterned etchmask layer 327 can overlie a segment of each memory stack structure 55within a neighboring pair of rows of memory stack structures 55. Eachmemory stack structure 55 of which a segment is located within an areaof one of the openings in the patterned etch mask layer 327 is hereinreferred to as a first memory stack structure 55A. Each memory openingfill structure 58 including a first memory stack structure 55A is hereinreferred to as a first memory opening fill structure 58A. Memory stackstructures 55 that are entirely covered with the patterned etch masklayer 327, for example, by being located between neighboring pairs offirst memory stack structures 55A, are herein referred to as a secondmemory stack structure 55B. Second memory stack structures 55B may, ormay not, be present in the first exemplary structure depending on thelayout of the elongated openings in the patterned etch mask layer 327.Each memory opening fill structure 58 including a second memory stackstructure 55B is herein referred to as a second memory opening fillstructure 58B.

Each first memory stack structure 55A is only partly covered with thepatterned etch mask layer 327. As such, a first area of each of thefirst memory stack structures 55A is located within an area of anelongated opening in the patterned etch mask layer 327, and a secondarea of each of the first memory stack structures 55A is covered by thepatterned etch mask layer 327. The first area can be in a range from 15%to 70%, such as from 25% to 50%, of the entire area of each first memorystack structure 55A.

An anisotropic etch process is performed to etch unmasked portions ofthe insulating cap layer 70 and upper layers of the alternating stack(32, 42) located at the drain select levels without etching the memorystack structures 55. A drain-select-level trench 309 is formedunderneath each elongated opening within the patterned etch mask layer327 by etching through an upper portion of the alternating stack (32,42) selective to the physically exposed material portions of the memoryopening fill structures 58. Each drain-select-level trench 309 caninclude a pair of laterally undulating lengthwise sidewalls that extendgenerally along the first horizontal direction hd1. Each laterallyundulating lengthwise sidewall can include a laterally alternatingsequence of straight sidewall segments (that are sidewalls of theinsulating cap layer 70 and upper layers of the alternating stack (32,42)) and concave sidewall segments (that are sidewalls of the memoryopening fill structures 58). The depth of the drain-select-leveltrenches 309 can be selected such that the drain-select-level trenches309 vertically extend through each sacrificial material layer 42 locatedat drain select levels, i.e., levels in which the sacrificial materiallayers 42 are subsequently replaced with electrically conductive layersthat function as drain select level gate electrodes. Each verticalsemiconductor channel 60 of the memory stack structures 55 has a tubularconfiguration.

The chemistry of the anisotropic etch process can be selective to thematerials of the drain regions 63, the vertical semiconductor channels60, and the outer layer of the memory films 50. In one embodiment, theblocking dielectric layers 52 can include an aluminum oxide layer as anoutermost layer, and the anisotropic etch process may be selective toaluminum oxide. The anisotropic etch process partially physicallyexposes upper portions of sidewalls of two rows of the first memorystack structures 55A around each drain-select-level trench 309. Eachdrain-select-level trench 309 extends through an upper portion of thealternating stack (32, 42) and laterally extends between two rows offirst memory stack structures 55A. The memory stack structures 55includes first memory stack structures 55A that are partially exposed toa respective one of the drain-select-level trenches 309, and optionallyincludes second memory stack structures 55B that are masked with thepatterned etch mask layer 317 during formation of the drain-select-leveltrenches 309. Thus, sidewalls of the second memory stack structures 55Bare not physically exposed after formation of the drain-select-leveltrenches 309.

Referring to FIG. 45, the processing steps of FIGS. 40A and 40B can beperformed to implant dopants of the first conductivity type intosegments of vertical semiconductor channels 60 within the first memorystack structures 55A that are proximal to a respective one of thedrain-select-level trenches 309. Each vertical semiconductor channel 60within the first memory stack structures 55A (located within the firstmemory opening fill structures 58A) comprises a tubular section 60Tincluding dopants of the first conductivity type at the first atomicconcentration (which is the atomic concentration of dopants of the firstconductivity type as provided during formation of the first and secondsemiconductor channel layers (601, 602)), a first semi-tubular section60S overlying the tubular section 60T and including dopants of the firstconductivity type at the first atomic concentration, and a secondsemi-tubular section 60U overlying the tubular section 60T and laterallyadjoined to the first semi-tubular section 60S and including dopants ofthe first conductivity type at a second atomic concentration that isgreater than the first atomic concentration.

In one embodiment, the second atomic concentration can be in a rangefrom 5 times the first atomic concentration to 1.0×10⁵ times the firstatomic concentration. In a non-limiting illustrative example, the firstatomic concentration can be in a range from 1.0×10¹⁴/cm³ to1.0×10¹⁸/cm³, and the second atomic concentration can be in a range from1.0×10¹⁷/cm³ to 1.0×10¹⁹/cm³, although lesser and greater concentrationscan be used for each of the first atomic concentration and the secondatomic concentration. In one embodiment, the tubular section 60T of eachfirst memory stack structure 55A (within a respective one of the firstmemory opening fill structures 58A) can be located underneath ahorizontal plane including bottom surfaces of the drain-select-leveltrenches 309. Each tubular section 60T, each first semi-tubular section60S, and each second semi-tubular section 60U can include a respectiveportion derived from a first semiconductor channel layer 601 and arespective portion derived from a second semiconductor channel layer602. The second semi-tubular section 60U may additionally include carbonatoms, for example, at an atomic concentration in a range from1.0×10¹⁵/cm³ to 5.0×10¹⁷/cm³, and the first semi-tubular section 60S andthe tubular section 60T may be free of carbon atoms, e.g., at a tracelevel below 1.0×10¹⁴/cm³. Thus, the atomic concentration of carbon atomsin the second semi-tubular section 60U can be at least 10 times theatomic concentration of carbon atoms in the first semi-tubular region60S, and at least 10 times the atomic concentration of carbon atoms inthe tubular region 60T.

The memory stack structures 55 can include second memory stackstructures 55B extending through the alternating stack (32, 46). Each ofthe second memory stack structures 55B includes a respective secondmemory film 50 and a respective second vertical semiconductor channel60, and each second vertical semiconductor channel 60 can include aportion having a tubular configuration, extend through each electricallyconductive layer 46 in the alternating stack (32, 46), and includedopants of the first conductivity type at the first atomic concentrationthroughout an entire volume thereof. The portion having the tubularconfiguration can extend to the horizontal plane including the topsurfaces of the drain regions 63.

In one embodiment, each of the first semi-tubular sections 60S has ahorizontal cross-sectional shape of a first block arc that is invariantwith translation along a vertical direction hd1, and each of the secondsemi-tubular sections 60U has a horizontal cross-sectional shape of asecond block arc that is invariant with translation along the verticaldirection. As used herein, a “block arc” is a shape that is obtained bylimiting the azimuthal extent of a planar annular shape to less than 360degrees around the geometrical center of the planar annular shape (i.e.,the shape of an anulus within a Euclidean plane).

Dopants of the first conductivity type are collaterally implanted into asegment of each of the first drain regions 63 during implantation of thedopants of the first conductivity type into the implanted segments ofvertical semiconductor channels 60 (i.e., into the second semi-tubularsections 60U). The first drain regions 63 can contact an upper end of arespective one of the first semi-tubular sections 60S, contact an upperend of a respective one of the second semi-tubular sections 60U, andhave a doping of the second conductivity type that is the opposite ofthe first conductivity type. In one embodiment, each of the first drainregions 63 can include a first drain segment 631 consisting essentiallyof a semiconductor material and dopants of the second conductivity typeand contacting the upper end of the respective one of the firstsemi-tubular sections 60S, and a second drain segment 632 consistingessentially of the semiconductor material, dopants of the secondconductivity type, and dopants of the first conductivity type, andcontacting the upper end of the respective one of the secondsemi-tubular sections 60U. The atomic concentration of dopants of thefirst conductivity type in a second drain segment 632 is less than theatomic concentration of dopants of the second conductivity type in thesecond drain segment 632, and can be the less than the atomicconcentration of dopants of the first conductivity type in the secondsemi-tubular sections 60U. The patterned etch mask layer 327 can beremoved, for example, by ashing after formation of thedrain-select-level trenches 309.

Referring to FIG. 46, drain-select-level isolation structure 322 can beformed in each drain-select-level trench 309, for example, by depositinga dielectric material such as silicon oxide in the drain-select-leveltrenches 309. Excess portions of the dielectric material can be removedfrom above the horizontal plane including the top surface of theinsulating cap layer 70 by a planarization process, which can use arecess etch and/or chemical mechanical planarization. Eachdrain-select-level isolation structure 322 can be formed in adrain-select-level trench 309 on sidewalls of memory films 50 of thefirst memory stack structures 55A. Each drain-select-level isolationstructure 320 can include a pair of laterally-undulating sidewalls thatlaterally extend along the first horizontal direction hd1 and includinga laterally alternating sequence of straight sidewall segments andconcave sidewall segments. Each drain-select-level isolation structure322 can vertically extend through each electrically conductive layer 46within the alternating stack (32, 46) that is located at a drain selectlevel.

In one embodiment, the first memory stack structures 55A are arranged infirst rows that extend along the first horizontal direction hd1 and hasa uniform intra-row pitch p1 within each first row. The second memorystack structures 55B are arranged in second rows that extend along thefirst horizontal direction hd1 and have the uniform intra-row pitch p1within each second row. The first memory stack structures 55A and thesecond memory stack structures 55B are arranged as a two-dimensionalperiodic array in which each neighboring pair of rows among the firstrows and second rows has a uniform inter-row pitch p2.

Subsequently, the processing steps of FIGS. 9A and 9B can be performedto form a contact level dielectric layer 73 and backside trenches 79.

Referring to FIG. 47, the processing steps of FIGS. 10, 11A-11D, 12, 13Aand 13B can be performed to replace the sacrificial material layers 42with electrically conductive layers 46. The processing steps of FIGS.14A, 14B, 15A, and 15B can be subsequently performed to provide astructure that is substantially identical to the structure of FIGS.43A-43C.

Referring to all drawings of the fourth and fifth exemplary structuresand according to various embodiments of the present disclosure, athree-dimensional memory device is provided, which comprises: analternating stack of insulating layers 32 and electrically conductivelayers 46 located over a substrate (9, 10); and first memory stackstructures 55A extending through the alternating stack (32, 46), whereineach of the first memory stack structures 55A includes a respectivefirst memory film 50 and a respective first vertical semiconductorchannel 60, wherein each first vertical semiconductor channel 60comprises a tubular section 60T including dopants of a firstconductivity type at a first atomic concentration, a first semi-tubularsection 60S overlying the tubular section and including dopants of thefirst conductivity type at the first atomic concentration, and a secondsemi-tubular section 60U overlying the tubular section and laterallyadjoined to the first semi-tubular section 60S and including dopants ofthe first conductivity type at a second atomic concentration that isgreater than the first atomic concentration.

In one embodiment, the three-dimensional memory device comprisesdrain-select-level isolation structures 322 vertically extending throughan upper region of the alternating stack (32, 46) and laterallyextending along a first horizontal direction hd1, wherein each of thefirst memory stack structures 55A contacts a respective one of thedrain-select-level isolation structures 322.

In one embodiment, the tubular section 60T of each first verticalsemiconductor channel 60 is located underneath a horizontal planeincluding bottom surfaces of the drain-select-level isolation structures322.

In one embodiment, each of the drain-select-level isolation structures322 comprises a pair of laterally-undulating sidewalls; and each of thelaterally-undulating sidewalls comprises an alternating sequence ofstraight sidewall segments and concave sidewall segments that areadjoined among one another. In one embodiment, each of the concavesidewall segments contacts an outer surface of a respective one of thefirst memory films 50. In one embodiment, each of the secondsemi-tubular sections 60U is laterally spaced from a most proximal oneamong the drain-select-level isolation structures 322 by a uniformlateral spacing that is the same as a lateral thickness of one of thefirst memory films 50.

The various embodiments of the present disclosure can be used to providedrain-select-level isolation structures (320, 322) without disturbingthe periodicity of a two-dimensional array of memory stack structures(55A, 55B). First memory stack structures 55A contacting a respectiveone of the drain-select-level isolation structures (320, 322) andoptional second memory stack structures 55B that do not contact any ofthe drain-select-level isolation structures (320, 322) can be within asame periodic two-dimensional periodic array, thereby enabling reductionof footprint for a three-dimensional array of memory devices.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the disclosure is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the disclosure. Compatibility ispresumed among all embodiments that are not alternatives of one another.The word “comprise” or “include” contemplates all embodiments in whichthe word “consist essentially of” or the word “consists of” replaces theword “comprise” or “include,” unless explicitly stated otherwise. Wherean embodiment using a particular structure and/or configuration isillustrated in the present disclosure, it is understood that the presentdisclosure may be practiced with any other compatible structures and/orconfigurations that are functionally equivalent provided that suchsubstitutions are not explicitly forbidden or otherwise known to beimpossible to one of ordinary skill in the art. All of the publications,patent applications and patents cited herein are incorporated herein byreference in their entirety.

What is claimed is:
 1. A three-dimensional memory device comprising: analternating stack of insulating layers and electrically conductivelayers located over a substrate; first memory stack structures extendingthrough the alternating stack, wherein each of the first memory stackstructures includes a respective first memory film and a respectivefirst vertical semiconductor channel; and a drain-select-level isolationstructure having a pair of straight lengthwise sidewalls that extendalong a first horizontal direction and contact straight sidewalls of thefirst memory stack structures, wherein each first vertical semiconductorchannel comprises a tubular section that underlie a horizontal planeincluding a bottom surface of the drain-select-level isolation structureand a semi-tubular section overlying the tubular section and contactingthe drain-select-level isolation structure.
 2. The three-dimensionalmemory device of claim 1, wherein each of the first verticalsemiconductor channels comprises: a tubular vertical semiconductorchannel segment that extends through a first plurality of electricallyconductive layers of the alternating stack that are located under thehorizontal plane; and a semi-tubular vertical semiconductor channelsegment that overlies the tubular vertical semiconductor channel segmentand contacts a respective one of the pair of straight lengthwisesidewalls of the drain-select-level isolation structure.
 3. Thethree-dimensional memory device of claim 2, further comprising firstdielectric cores located within a respective one of the first memorystack structures, wherein each of the first dielectric cores comprises:a cylindrical core portion that extends through the first plurality ofelectrically conductive layers of the alternating stack that are locatedunder the horizontal plane; and a semi-cylindrical portion that overliesthe tubular vertical semiconductor channel segment and contacts arespective one of the pair of straight lengthwise sidewalls of thedrain-select-level isolation structure.
 4. The three-dimensional memorydevice of claim 2, wherein: the first vertical semiconductor channelshave a doping of a first conductivity type; and first drain regionshaving a doping of a second conductivity type are located at an upperend of each of the first vertical semiconductor channels.
 5. Thethree-dimensional memory device of claim 4, wherein each of the firstdrain regions has a straight sidewall that contacts a respective one ofthe pair of straight lengthwise sidewalls of the drain-select-levelisolation structure.
 6. The three-dimensional memory device of claim 1,wherein the drain-select-level isolation structure vertically extendsthrough a plurality of electrically conductive layers including atopmost one of the electrically conductive layers within the alternatingstack.
 7. The three-dimensional memory device of claim 1, wherein: thedrain-select-level isolation structure vertically extends through atopmost one of the electrically conductive layers within the alternatingstack; the topmost one of the electrically conductive layers comprises adrain-select-level metallic liner and a drain-select-level metal fillportion embedded within the drain-select-level metallic liner; and adielectric layer contacts top surfaces of the drain-select-levelmetallic liner and the drain-select-level metal fill portion.
 8. Thethree-dimensional memory device of claim 1, wherein: the substratecomprises a semiconductor material layer; the semiconductor materiallayer and the first vertical semiconductor channels have a doping of afirst conductivity type; pedestal channel portions are disposed betweenbottom ends of the first vertical semiconductor channels and thesemiconductor material layer; and a source region having a doping of asecond conductivity type is embedded within the semiconductor materiallayer and is laterally spaced from the first memory stack structures andthe pedestal channel portions.
 9. The three-dimensional memory device ofclaim 1, wherein: the first vertical semiconductor channels have adoping of a first conductivity type; a source contact layer having adoping of a second conductivity type that is an opposite of the firstconductivity type is located over the substrate; and the source contactlayer contacts bottom ends of each of the first vertical semiconductorchannels.
 10. The three-dimensional memory device of claim 1, furthercomprising second memory stack structures extending through thealternating stack, wherein: each of the second memory stack structuresincludes a respective second memory film and a respective secondvertical semiconductor channel; and each second vertical semiconductorchannel includes a portion having a tubular configuration and extendingthrough each electrically conductive layer in the alternating stack. 11.The three-dimensional memory device of claim 10, wherein: the firstmemory stack structures are arranged in first rows that extend along afirst horizontal direction and have a uniform intra-row pitch withineach first row; the second memory stack structures are arranged insecond rows that extend along the first horizontal direction and havethe uniform intra-row pitch within each second row; and the first memorystack structures and the second memory stack structures are arranged asa two-dimensional periodic array in which each neighboring pair of rowsamong the first rows and second rows has a uniform inter-row pitch. 12.The three-dimensional memory device of claim 11, further comprising apair of backside trenches vertically extending through the alternatingstack and laterally extending along the first horizontal direction,wherein the two-dimensional periodic array and the drain-select-levelisolation structure are located between the pair of backside trenches.13. The three-dimensional memory device of claim 10, further comprising:first drain regions contacting an upper end of a respective one of thefirst vertical semiconductor channels and having a semi-cylindricalshape; second drain regions contacting an upper end of a respective oneof the second vertical semiconductor channels and having a cylindricalshape; first drain contact via structures having bottommost surfacesthat contact topmost surfaces of the first drain regions; and seconddrain contact via structures contacting a top surface and a sidewall ofa respective one of the second drain regions.
 14. A method of forming athree-dimensional memory device, comprising: forming an alternatingstack of insulating layers and spacer material layers over a substrate,wherein the spacer material layers are formed as, or are subsequentlyreplaced with, electrically conductive layers; forming memory stackstructures extending through the alternating stack, wherein each of thememory stack structures includes a respective memory film and arespective vertical semiconductor channel including dopants of a firstconductivity type, wherein the memory stack structures comprise firstmemory stack structures arranged in two rows that extend along a firsthorizontal direction; forming a drain-select-level trench by etchingthrough an upper portion of the alternating stack and a first area ofeach of the first memory stack structures, wherein thedrain-select-level trench includes a pair of straight lengthwisesidewalls that extend along the first horizontal direction; and forminga drain-select-level isolation structure in the drain-select-leveltrench, wherein each vertical semiconductor channel within the firstmemory stack structures comprises: a tubular section that underlies ahorizontal plane including a bottom surface of the drain-select-levelisolation structure; and a semi-tubular section overlying the tubularsection and contacting the drain-select-level isolation structure. 15.The method of claim 14, further comprising: forming a patterned etchmask layer including an elongated opening over the alternating stack andthe memory stack structures, wherein the first area of each of the firstmemory stack structures is located within an area of the elongatedopening and a second area of each of the first memory stack structuresis covered by the patterned etch mask layer; and performing ananisotropic etch process that etches the upper portion of thealternating stack and at least portions of vertical semiconductorchannels of the first memory stack structures that are not masked by thepatterned etch mask layer.
 16. The method of claim 15, wherein theanisotropic etch process etches portions of memory films of the firstmemory stack structure that underlie the elongated opening in thepatterned etch mask layer.
 17. The method of claim 15, furthercomprising removing portions of memory films of the first memory stackstructure that underlie the elongated opening by performing an isotropicetch process after performing the anisotropic etch process.
 18. Themethod of claim 14, further comprising: forming drain regions having adoping of a second conductivity type that is an opposite of the firstconductivity type on an upper end of each of the vertical semiconductorchannels, wherein the drain regions comprise first drain regions thatcontact a respective one of the first memory stack structures; andremoving a portion of each first drain region during formation of thedrain-select-level trench, wherein the pair of straight lengthwisesidewalls of the drain-select-level trench comprise straight sidewallsegments of remaining portions of the first drain regions.
 19. Themethod of claim 14, wherein: the memory stack structures comprise secondmemory stack structures that are masked with a patterned etch mask layerduring formation of the drain-select-level trench such that sidewalls ofthe second memory stack structures are not etched during formation ofthe drain-select-level trench; and each vertical semiconductor channelof the second memory stack structures includes a portion having atubular configuration and extending through each electrically conductivelayer in the alternating stack.
 20. The method of claim 19, wherein: thefirst memory stack structures within the two rows have a uniformintra-row pitch; the second memory stack structures are arranged in rowsthat extend along the first horizontal direction with the uniformintra-row pitch; and the first memory stack structures and the secondmemory stack structures are arranged as a two-dimensional periodic arrayin which each neighboring pair of rows of memory stack structures has auniform inter-row pitch.